Move build from workflow job to container action

I've changed the setup of the natives-linux job to not require needing Node 20, so hopefully it will continue to work with newer versions of checkout and upload-artifact for the forseeable future. I've done this by moving the docker setup into its own action (which is local to the repo) that runs a script in the container that builds the natives and snapshots, but doesn't use any third party actions - meaning it should not be need node 20 to be used in the container.

Other minor changes:

- Used apt-get instead of apt because using apt in a script gives the warning message "apt does not have a stable interface".
- Removed usages of sudo just to be consistent (I can't always use sudo because initially sudo isn't installed)
- Added --no-daemon to gradle command because only one gradle command is being run so the daemon isn't necessary.
- Added --quiet to apt-get usages to cut down unuseful lines in logs
- Moved around arguments to apt-get so they're always at the front
- removed setup-java and gradle-build-action usages in the natives-linux step because zulu installation is done in the container and gradle is downloaded when the wrapper is run.
- gnupg gets installed anyway as a dependency but I added it explicitly because it is needed for dearmoring the azul key

Having the action be in a separate actions folder may not be desirable, in which case I can probably move the action into the workflow folder somewhere but I'm not sure where.

Copied docker action structure from my similar PR in Jamepad (libgdx/Jamepad#34)

.github/actions/build-linux-natives/Dockerfile

@@ -0,0 +1,8 @@
+# Container image that runs your code
+FROM ubuntu:18.04
+
+# Copies your code file from your action repository to the filesystem path `/` of the container
+COPY entrypoint.sh /entrypoint.sh
+
+# Code file to execute when the docker container starts up (`entrypoint.sh`)
+ENTRYPOINT ["/entrypoint.sh"]

.github/actions/build-linux-natives/action.yml

@@ -0,0 +1,6 @@
+# action.yml
+name: 'Build Linux Natives in Docker Container'
+description: 'Build Linux Natives in Ubuntu 18.04 docker container'
+runs:
+  using: 'docker'
+  image: 'Dockerfile'

.github/actions/build-linux-natives/entrypoint.sh

@@ -0,0 +1,44 @@
+#!/bin/sh -l
+
+# ubuntu dockerfile is very minimal (only 122 packages are installed)
+# need to install updated git (from official git ppa)
+apt-get -q update
+apt-get -yq install software-properties-common
+add-apt-repository ppa:git-core/ppa -y
+# install dependencies expected by other steps
+apt-get -q update
+apt-get -yq install git \
+curl \
+ca-certificates \
+wget \
+bzip2 \
+zip \
+unzip \
+xz-utils \
+sudo gnupg locales
+
+# set Locale to en_US.UTF-8 (avoids hang during compilation)
+locale-gen en_US.UTF-8
+export LANG=en_US.UTF-8
+export LANGUAGE=en_US.UTF-8
+export LC_ALL=en_US.UTF-8
+
+# add zulu apt repository - https://docs.azul.com/core/install/debian
+curl -s https://repos.azul.com/azul-repo.key | gpg --dearmor -o /usr/share/keyrings/azul.gpg
+echo "deb [signed-by=/usr/share/keyrings/azul.gpg] https://repos.azul.com/zulu/deb stable main" | tee /etc/apt/sources.list.d/zulu.list
+apt-get -q update
+# install zulu JDK and Java build tools
+apt-get -yq install zulu17-jdk-headless maven ant
+
+# Install cross-compilation toolchains
+apt-get -yq --force-yes install gcc g++
+apt-get -yq --force-yes install gcc-aarch64-linux-gnu g++-aarch64-linux-gnu libc6-dev-arm64-cross
+apt-get -yq --force-yes install gcc-arm-linux-gnueabihf g++-arm-linux-gnueabihf libc6-dev-armhf-cross
+apt-get -yq --force-yes install gcc-riscv64-linux-gnu g++-riscv64-linux-gnu libc6-dev-riscv64-cross
+
+# Build Linux natives
+./gradlew jniGen jnigenBuildLinux64 jnigenBuildLinuxARM jnigenBuildLinuxARM64 jnigenBuildLinuxRISCV64 --no-daemon
+
+# Pack artifacts
+find .  -name "*.a" -o -name "*.dll" -o -name "*.dylib" -o -name "*.so" | grep "libs" > native-files-list
+zip natives-linux -@ < native-files-list

.github/workflows/build-publish.yml

@@ -8,9 +8,6 @@ on:
   release:
     types: [ published ]
 
-env:
-  ACTIONS_ALLOW_USE_UNSECURE_NODE_VERSION: true
-
 jobs:
 
   natives-ios:
@@ -92,65 +89,15 @@ jobs:
 
   natives-linux:
     runs-on: ubuntu-20.04
-    container:
-      image: ubuntu:18.04
     steps:
-      - name: Install dependencies into minimal dockerfile
-        run: |
-          # ubuntu dockerfile is very minimal (only 122 packages are installed)
-          # need to install updated git (from official git ppa)
-          apt update
-          apt install -y software-properties-common
-          add-apt-repository ppa:git-core/ppa -y
-          # install dependencies expected by other steps
-          apt update
-          apt install -y git \
-          curl \
-          ca-certificates \
-          wget \
-          bzip2 \
-          zip \
-          unzip \
-          xz-utils \
-          maven \
-          ant sudo locales
-
-          # set Locale to en_US.UTF-8 (avoids hang during compilation)
-          locale-gen en_US.UTF-8
-          echo "LANG=en_US.UTF-8" >> $GITHUB_ENV
-          echo "LANGUAGE=en_US.UTF-8" >> $GITHUB_ENV
-          echo "LC_ALL=en_US.UTF-8" >> $GITHUB_ENV
-
       - uses: actions/checkout@v2
         with:
           fetch-depth: 0
           submodules: 'recursive'
 
-      - name: Set up JDK 17
-        uses: actions/setup-java@v3
-        with:
-          distribution: 'zulu'
-          java-version: '17'
-
-      - name: Setup Gradle
-        uses: gradle/gradle-build-action@v2
-
-      - name: Install cross-compilation toolchains
-        run: |
-          sudo apt update
-          sudo apt install -y --force-yes gcc g++
-          sudo apt install -y --force-yes gcc-aarch64-linux-gnu g++-aarch64-linux-gnu libc6-dev-arm64-cross
-          sudo apt install -y --force-yes gcc-arm-linux-gnueabihf g++-arm-linux-gnueabihf libc6-dev-armhf-cross
-          sudo apt install -y --force-yes gcc-riscv64-linux-gnu g++-riscv64-linux-gnu libc6-dev-riscv64-cross
-
-      - name: Build Linux natives
-        run: |
-          ./gradlew jniGen jnigenBuildLinux64 jnigenBuildLinuxARM jnigenBuildLinuxARM64 jnigenBuildLinuxRISCV64
-
-      - name: Pack artifacts
-        run: |
-          find .  -name "*.a" -o -name "*.dll" -o -name "*.dylib" -o -name "*.so" | grep "libs" > native-files-list
-          zip natives-linux -@ < native-files-list
+      - name: Build Linux Natives in Docker Container
+        uses: ./.github/actions/build-linux-natives
+        id: docker
 
       - name: Upload artifacts
         uses: actions/upload-artifact@v3