[ci] Use coveralls action instead of Python package

coveralls Python package is not updated since 2021 and doesn't
support Python 3.11. Use the coveralls GitHub action instead.

Signed-off-by: Jose Javier Merchante <jjmerchante@bitergia.com>

.github/workflows/tests.yml

@@ -31,7 +31,6 @@ jobs:
       - name: Install dependencies
         run: |
           poetry install -vvv
-          poetry add -D coveralls
       - name: Lint with flake8
         run: |
           poetry run flake8
@@ -41,4 +40,5 @@ jobs:
         run: |
           cd tests
           poetry run coverage run --source=perceval run_tests.py
-          poetry run coveralls --service=github
+      - name: Coveralls
+        uses: coverallsapp/github-action@f350da2c033043742f89e8c0b7b5145a1616da6d # v2.1.2