make core test sequential temporarily

Author: amanjaiswal73892

.github/workflows/unit_tests.yml

@@ -118,7 +118,7 @@ jobs:
         run: playwright install chromium --with-deps
 
       - name: Run browsergym-core Unit Tests
-        run: pytest -n 5 --durations=10 -m 'not pricy' -v tests/core
+        run: pytest -n 1 --durations=10 -m 'not pricy' -v tests/core
 
   browsergym-miniwob:
     runs-on: ubuntu-22.04