Add basic macos bazel test workflow

.github/workflows/bazel_test_post_merge.yml

@@ -0,0 +1,16 @@
+name: Bazel Test (Post-Merge)
+
+on:
+  push:
+    branches:
+      - master
+
+jobs:
+  trigger-win-latest-test:
+    # This prevents the workflow from running automatically when someone
+    # pushes to their fork.
+    if: github.repository == 'cel-expr/cel-cpp'
+    uses: ./.github/workflows/windows_bazel_test.yml
+  trigger-mac-latest-test:
+    if: github.repository == 'cel-expr/cel-cpp'
+    uses: ./.github/workflows/macos_bazel_test.yml

.github/workflows/macos_bazel_test.yml

@@ -0,0 +1,26 @@
+name: MacOS Bazel Test
+
+on:
+  workflow_call:
+  workflow_dispatch:
+
+jobs:
+  test:
+    name: Run Bazel Tests
+    runs-on: macos-latest
+    steps:
+      - name: Checkout Repository
+        uses: actions/checkout@v4
+
+      - name: Setup Bazel and Bazelisk
+        uses: bazel-contrib/setup-bazel@0.19.0
+        with:
+          bazelisk-cache: true
+          disk-cache: ${{ github.workflow }}
+          repository-cache: true
+
+      - name: Run Tests
+        shell: bash
+        # TODO: <filesystem> is not supported on all target versions in xcode, so not running policy conformance.
+        run: |
+          bazelisk test --copt=-Wno-deprecated-declarations --copt=-Wno-nullability-completeness conformance:all

.github/workflows/windows_bazel_test.yml

@@ -25,4 +25,4 @@ jobs:
         # //... won't work.
         shell: bash
         run: |
-          bazelisk test --config=msvc conformance:all conformance/policy:all
+          bazelisk test --config=msvc conformance:all conformance/policy:all