chore: enable some CI on macos again

We need at least some coverage, even if we don't have a container runtime there

.github/workflows/ci.yaml

@@ -29,16 +29,34 @@ jobs:
       # Will look like ["<version from .bazelversion>", "5.3.2"]
       bazelversions: ${{ toJSON(steps.*.outputs.bazelversion) }}
 
+    matrix-prep-os:
+      # Prepares the 'os' axis of the test matrix
+      runs-on: ubuntu-latest
+      env:
+        TC_CLOUD_TOKEN: ${{ secrets.TC_CLOUD_TOKEN }}
+      steps:
+        - id: linux
+          run: echo "os=ubuntu-latest" >> $GITHUB_OUTPUT
+        - id: rbe
+          run: echo "os=macos-latest" >> $GITHUB_OUTPUT
+          # Don't run MocOS if there is no TestContainers API token which is the case on forks
+          # We expect to use it at some point for tests that need a docker daemon.
+          if: ${{ env.TC_CLOUD_TOKEN != '' }}
+      outputs:
+        # Will look like ["ubuntu-latest", "macos-latest"]
+        os: ${{ toJSON(steps.*.outputs.os) }}
+
   test:
     # The type of runner that the job will run on
     runs-on: ${{ matrix.os }}
     needs:
       - matrix-prep-bazelversion
+      - matrix-prep-os
 
     strategy:
       fail-fast: false
       matrix:
-        os: [ubuntu-latest]
+        os: ${{ fromJSON(needs.matrix-prep-os.outputs.os) }}
         bazelversion: ${{ fromJSON(needs.matrix-prep-bazelversion.outputs.bazelversions) }}
         folder:
           - .