chore: attempt to speed up tests

Author: parthea

.github/workflows/unittest.yml

@@ -36,7 +36,7 @@ jobs:
         # such as grpcio, which we build from scratch on every run for Python 3.15+.
         # Follow https://github.com/grpc/grpc/issues/41010 for updates.
         cache: 'pip'
-        cache-dependency-path: '**/constraints*.txt'
+        cache-dependency-path: 'packages/**/testing/constraints*.txt'
     - name: Install nox
       run: |
         python -m pip install --upgrade setuptools pip wheel