Try to fix coveralls github action that fails to upload results

It says:
HTTPError: 422 Client Error: Unprocessable Entity for url: https://coveralls.io/api/v1/jobs

Fix according to:
https://stackoverflow.com/questions/65692711/using-python-coveralls-from-github-actions-returns-could-not-submit-coverage-4

Author: wonder-sk

.github/workflows/autotests.yml

@@ -30,4 +30,4 @@ jobs:
         env:
           GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
         run: |
-          coveralls
+          coveralls --service=github