github: fix coveralls

Just having the toml package installed is no longer enough. We have to
install coverage with toml as an extra.

Related: TheKevJames/coveralls-python#335

Author: dlech

.github/workflows/test.yml

@@ -25,7 +25,7 @@ jobs:
       - run: poetry run coverage run
       - run: |
           pipx install coveralls
-          pipx inject coveralls toml
+          pipx inject coveralls coverage[toml]
       - run: coveralls --service=github
         env:
           GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}