Fix Synapse docker builds again. (#1339)

By only using the --break-system-packages on the versions
which support it.

.github/workflows/docker.yml

@@ -12,6 +12,10 @@ on:
 permissions:
   contents: read
 
+concurrency:
+  group: ${{ github.workflow }}-${{ github.ref }}
+  cancel-in-progress: true
+
 jobs:
   build-sytest-images:
     name: "Build sytest:${{ matrix.tag }}"
@@ -25,8 +29,6 @@ jobs:
             tag: buster
           - base_image: debian:testing
             tag: testing
-          - base_image: debian:bookworm
-            tag: bookworm
     steps:
       - name: Set up QEMU
         id: QEMU
@@ -74,11 +76,9 @@ jobs:
           - sytest_image_tag: testing
             dockerfile: synapse
             tags: "matrixdotorg/sytest-synapse:testing"
-            build_args: "SYTEST_IMAGE_TAG=testing"
-          - sytest_image_tag: bookworm
-            dockerfile: synapse
-            tags: "matrixdotorg/sytest-synapse:bookworm"
-            # Note: at the time of writing, bookworm's python3 is python 3.11.
+            build_args: |
+              SYTEST_IMAGE_TAG=testing
+              SYSTEM_PIP_INSTALL_SUFFIX=--break-system-packages
 
     steps:
       - name: Set up QEMU

docker/synapse.Dockerfile

@@ -3,6 +3,7 @@ ARG SYTEST_IMAGE_TAG=buster
 FROM matrixdotorg/sytest:${SYTEST_IMAGE_TAG}
 
 ARG PYTHON_VERSION=python3
+ARG SYSTEM_PIP_INSTALL_SUFFIX=""
 
 ENV DEBIAN_FRONTEND noninteractive
 
@@ -26,8 +27,8 @@ RUN curl -sSf https://sh.rustup.rs | sh -s -- -y --no-modify-path --default-tool
 # For now, we need to tell Debian we don't care that we're editing the system python
 # installation.
 # Some context in https://github.com/pypa/pip/issues/11381#issuecomment-1399263627
-RUN ${PYTHON_VERSION} -m pip install -q --upgrade pip --break-system-packages
-RUN ${PYTHON_VERSION} -m pip install -q --no-cache-dir poetry==1.3.2 --break-system-packages
+RUN ${PYTHON_VERSION} -m pip install -q --upgrade pip ${SYSTEM_PIP_INSTALL_SUFFIX}
+RUN ${PYTHON_VERSION} -m pip install -q --no-cache-dir poetry==1.3.2 ${SYSTEM_PIP_INSTALL_SUFFIX}
 
 # As part of the Docker build, we attempt to pre-install Synapse's dependencies
 # in the hope that it speeds up the real install of Synapse. To make this work,