ci: set up Go in release platform smoke

[tonyredondo]

Summary

Adds the same Go toolchain setup used by CI to the release platform smoke job.

The pre-tag release gate failed on macOS before running the mock-server harness because go was not available on the runner. The harness requires a host Go binary for the bootstrap integration path.

Validation

python3 tools/dev/check_module_versions.py
git diff --check
bash -n tools/tests/integration/run_mock_server_tests.sh tools/tests/integration/run_bzlmod_go_integration.sh tools/tests/integration/run_workspace_go_integration.sh
python3 - <<'PY'
from pathlib import Path
text = Path(".github/workflows/release.yml").read_text()
for needle in ["GO_VERSION: \"1.25.0\"", "actions/setup-go@4a3601121dd01d1626a1e23e37211e3254c1c06c", "go-version: ${{ env.GO_VERSION }}"]:
    if needle not in text:
        raise SystemExit(f"missing {needle}")
print("release workflow Go setup present")
PY

Release workflow validation will be rerun on this branch before tagging v1.0.0.

Release Readiness

• Updated user-facing docs for behavior or API changes. Not applicable: CI-only release gate fix.
• Updated LICENSE-3rdparty.csv when dependencies or vendored code changed. Not applicable.
• Confirmed no secrets, credentials, or internal-only details were added.