ci: use --frozen-lockfile in yarn install

Author: snitin315

.github/workflows/testing.yml

@@ -79,7 +79,7 @@ jobs:
           node-version: ${{ matrix.node-version }}
           cache: yarn
 
-      - run: yarn
+      - run: yarn --frozen-lockfile
 
       - name: Enable webpack persistent caching
         uses: ./.github/actions/webpack-persistent-cache