ci: filter macOS walltime jobs to BM_FibonacciRecursive_Darwin

Author: not-matthias

.github/workflows/ci.yml

@@ -255,6 +255,7 @@ jobs:
           # This is because bazel does not like the user switch between running `bazel build` as a user then running `bazel run` as sudo and refuses to run.
           # For now, `$USER` remains the original user, but the program is ran with uid 0 with `sudo --preserve-env`
           # This problem is temporary because the runner does not YET do the same uid/gid spoofing on macos as it does on linux.
+          #
           # BUILD_WORKSPACE_DIRECTORY is normally set by `bazel run`; we set it manually so workspace-relative __FILE__ resolution works when invoking the binary directly.
           run: BUILD_WORKSPACE_DIRECTORY=$PWD ./bazel-bin/examples/google_benchmark_bazel/my_benchmark --benchmark_filter=BM_FibonacciRecursive_Darwin
           mode: walltime