Explicitly enable workspace when bzlmod is disabled in examples tests.

Note in Bazel 8 --enable_workspace is now false by default, which is probably why  continuous tests fail when testing with bzlmod disabled: https://github.com/protocolbuffers/protobuf/actions/runs/12274024400/job/34246134153

`bazelversion` here also doesn't seem to be applied as Bazel 8 is being used based on the logs.

#test-continuous

PiperOrigin-RevId: 705140770

.github/workflows/test_bazel.yml

@@ -58,4 +58,4 @@ jobs:
           credentials: ${{ secrets.GAR_SERVICE_ACCOUNT }}
           bazel-cache: examples
           version: ${{ matrix.bazelversion }}
-          bash: cd examples && bazel build //... $BAZEL_FLAGS --enable_bzlmod=${{ matrix.bzlmod }} ${{ matrix.toolchain_resolution }}
+          bash: cd examples && bazel build //... $BAZEL_FLAGS --enable_bzlmod=${{ matrix.bzlmod }} --enable_workspace=${{ !matrix.bzlmod }} ${{ matrix.toolchain_resolution }}