chore(python): update unittest workflow template (#2008)

* fix: update unittest workflow template

* undo if-no-files-found

Author: chelsea-lin

synthtool/gcp/templates/python_library/.github/workflows/unittest.yml

@@ -30,6 +30,7 @@ jobs:
       with:
         name: coverage-artifact-${{ '{{' }} matrix.python {{ '}}' }}
         path: .coverage-${{ '{{' }} matrix.python {{ '}}' }}
+        include-hidden-files: true
 
   cover:
     runs-on: ubuntu-latest