Run downstream tests: ArchGDAL (#154)

Since ArchGDAL has much more extensive tests, this will catch more issues. Fixes #144.

Also adds dependabot to keep the GitHub Actions up to date, as done here: SciML/MuladdMacro.jl#37

.github/dependabot.yml

@@ -0,0 +1,7 @@
+# https://docs.github.com/github/administering-a-repository/configuration-options-for-dependency-updates
+version: 2
+updates:
+  - package-ecosystem: "github-actions"
+    directory: "/" # Location of package manifests
+    schedule:
+      interval: "weekly"

.github/workflows/IntegrationTest.yml

@@ -0,0 +1,54 @@
+name: IntegrationTest
+on:
+  push:
+    branches: [master]
+    tags: [v*]
+  pull_request:
+
+concurrency:
+  # Skip intermediate builds: always.
+  # Cancel intermediate builds: only if it is a pull request build.
+  group: ${{ github.workflow }}-${{ github.ref }}
+  cancel-in-progress: ${{ startsWith(github.ref, 'refs/pull/') }}
+
+jobs:
+  test:
+    name: ${{ matrix.package.repo }}
+    runs-on: ${{ matrix.os }}
+    strategy:
+      fail-fast: false
+      matrix:
+        julia-version: [1]
+        os: [ubuntu-latest]
+        package:
+          - {user: yeesian, repo: ArchGDAL.jl}
+
+    steps:
+      - uses: actions/checkout@v3
+      - uses: julia-actions/setup-julia@v1
+        with:
+          version: ${{ matrix.julia-version }}
+          arch: x64
+      - uses: julia-actions/julia-buildpkg@v1
+      - name: Clone Downstream
+        uses: actions/checkout@v3
+        with:
+          repository: ${{ matrix.package.user }}/${{ matrix.package.repo }}
+          path: downstream
+      - name: Load this and run the downstream tests
+        shell: julia --project=downstream {0}
+        run: |
+          using Pkg
+          try
+            # Force downstream tests to use this PR's version of the package.
+            Pkg.develop(PackageSpec(path="."))  # resolver may fail with main deps
+            Pkg.update()
+            Pkg.test()  # resolver may fail with test time deps
+          catch err
+            err isa Pkg.Resolve.ResolverError || rethrow()
+            # If we can't resolve that means this is incompatible by SemVer and this is fine;
+            # it means we marked this as a breaking change, so we don't need to worry about
+            # mistakenly introducing a breaking change, as we have intentionally made one
+            @info "Not compatible with this release. No problem." exception=err
+            exit(0)  # Exit immediately as a success.
+          end