message: Cache clang-tidy results.
  clang-tidy takes almost 30min in the CI, so let's remember the
  content hashes of all files we processed so that we only have to
  look at changed files.
diff: @@ -60,6 +60,22 @@ jobs:
  - name: Install Dependencies
  run: |
  sudo apt -qq -y install clang-tidy-12
  + echo "TMPDIR=/tmp" >> $GITHUB_ENV
  +
  + - name: Create Cache Timestamp
  + id: cache_timestamp
  + uses: nanzm/get-time-action@v1.1
  + with:
  + format: 'YYYY-MM-DD-HH-mm-ss'
  +
  + - name: Retrieve cached results
  + uses: actions/cache@v2
  + with:
  + path: |
  + /tmp/clang-tidy-hashes.cache
  + /home/runner/.cache/bazel
  + key: clang-tidy-${{ steps.cache_timestamp.outputs.time }}
  + restore-keys: clang-tidy-
  - name: Run clang tidy
  run: ./.github/bin/run-clang-tidy.sh
  