message: chore(ci): prepare yarn cache for all 3 OSes
  Not really necessary, but default cache key for GH Actions includes the
  OS name.
diff: @@ -19,7 +19,11 @@ jobs:
  prepare-yarn-cache:
  name: Prepare yarn cache
  - runs-on: ubuntu-latest
  + strategy:
  + fail-fast: false
  + matrix:
  + os: [ubuntu-latest, macOS-latest, windows-latest]
  + runs-on: ${{ matrix.os }}
  steps:
  - uses: actions/checkout@v2
  