fix(ci): update 'PARALLEL_TOTAL' from 9 to 15

Author: nicholaschiang

.github/workflows/tests.yml

@@ -7,7 +7,7 @@ on:
 env:
   NODE_ENV: test
   PERCY_PARALLEL_NONCE: github.token
-  PERCY_PARALLEL_TOTAL: 9
+  PERCY_PARALLEL_TOTAL: 15
   ALGOLIA_ADMIN_KEY: ${{ secrets.ALGOLIA_ADMIN_KEY }}
   CYPRESS_RECORD_KEY: ${{ secrets.CYPRESS_RECORD_KEY }}
   FIREBASE_ADMIN_CLIENT_EMAIL: ${{ secrets.FIREBASE_ADMIN_CLIENT_EMAIL }}