Ensure test-firefox-safari is required for tests passing (vercel#63733)

This can currently fail and still pass our final tests pass check which
it shouldn't

x-ref: vercel#63726

Closes NEXT-2939

.github/workflows/build_and_test.yml

@@ -424,6 +424,7 @@ jobs:
         'test-dev',
         'test-prod',
         'test-integration',
+        'test-firefox-safari',
         'test-ppr-dev',
         'test-ppr-prod',
         'test-ppr-integration',