Updated yarn command to use --frozen-lockfile

ref yarnpkg/yarn#4147

- Running yarn install without --frozen-lockfile can result in the
yarn.lock file being mutated during the build step
- This means discrepancies between package.json and yarn.lock are
handled silently in CI and not caught until the deployment states later
- By adding --frozen-lockfile to our test build, we'll ensure these
types of issues are caught earlier

Author: ErisDS

.github/workflows/test.yml

@@ -34,7 +34,7 @@ jobs:
       - run: yarn global add lerna@^4
         if: steps.check_files.outputs.files_exists == 'true'
 
-      - run: yarn --prefer-offline
+      - run: yarn --prefer-offline --frozen-lockfile
       - run: yarn test
 
       - uses: codecov/codecov-action@v3