Drop Bazel 4 support and add Bazel 6

PiperOrigin-RevId: 539130329

.github/workflows/test_cpp.yml

@@ -36,9 +36,10 @@ jobs:
           - config: { name: "aarch64" }
             targets: "//src/... //src/google/protobuf/compiler:protoc_aarch64_test"
             image: "us-docker.pkg.dev/protobuf-build/containers/test/linux/emulation:aarch64-3af05275178e16af30961976af126eabbbb2c733"
-          - config: { name: "Bazel4" }
+          # TODO(b/278116805) Enable this once Bazel 6 is supported.
-            targets: "//src/..."
+          #- config: { name: "Bazel6" }
-            image: "us-docker.pkg.dev/protobuf-build/containers/common/linux/bazel:4.2.3-6361b3a6e5c97e9951d03a4de28542fc45f1adab"
+          #  targets: "//src/..."
+          #  image: "us-docker.pkg.dev/protobuf-build/containers/common/linux/bazel:6.0.0-6361b3a6e5c97e9951d03a4de28542fc45f1adab"
     name: Linux ${{ matrix.config.name }}
     runs-on: ubuntu-latest
     steps: