Faster pancakes: cache bazel steps between builds (#26937)

* cache bazel steps

* test break

* Automated change: Fix sanity tests

Co-authored-by: ctiller <ctiller@users.noreply.github.com>

.github/workflows/pr-auto-fix.yaml

@@ -4,6 +4,14 @@ jobs:
   PRAutoFix:
     runs-on: ubuntu-latest
     steps:
+      # Cache bazel build
+      - name: Cache bazel
+        uses: actions/cache@v2
+        env:
+          cache-name: bazel-cache
+        with:
+          path: ~/.cache/bazel
+          key: ${{ runner.os }}-${{ env.cache-name }}
       # Cancel current runs if they're still running
       # (saves processing on fast pushes)
       - name: Cancel Previous Runs