cache yarn for flakey test workflow

Author: billyvg

.github/workflows/flaky-test-detector.yml

@@ -35,6 +35,7 @@ jobs:
         uses: actions/setup-node@v3
         with:
           node-version-file: 'package.json'
+          cache: 'yarn'
       - name: Install dependencies
         run: yarn install --ignore-engines --frozen-lockfile