chore: fix the test cover workflow (#948)

* chore: fix the test cover workflow

* try absolute paths

* tag to old version

* include-hidden-files

* 🦉 Updates from OwlBot post-processor

See https://github.com/googleapis/repo-automation-bots/blob/main/packages/owl-bot/README.md

* exclude unitest.yml in owlbot.py

---------

Co-authored-by: Owl Bot <gcf-owl-bot[bot]@users.noreply.github.com>

Author: chelsea-lin

.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

owlbot.py

@@ -49,6 +49,7 @@
         "README.rst",
         "CONTRIBUTING.rst",
         ".github/release-trigger.yml",
+        ".github/workflows/unittest.yml",
         # BigQuery DataFrames manages its own Kokoro cluster for presubmit & continuous tests.
         ".kokoro/build.sh",
         ".kokoro/continuous/common.cfg",