Temporarily use the PR branch of the cache action

Author: aomarks

.github/workflows/tests.yml

@@ -54,7 +54,10 @@ jobs:
           node-version: ${{ matrix.node }}
           cache: npm
 
-      - uses: google/wireit@setup-github-actions-caching/v2
+      # TODO(aomarks) Switch back to the regular reference after the tag is
+      # updated.
+      # - uses: google/wireit@setup-github-actions-caching/v2
+      - uses: google/wireit@gh-cache-real-action
 
       - run: npm ci