ci: switch to GITHUB_TOKEN for public repo Coveralls integration

Author: harryswift01

.github/workflows/project-ci.yaml

@@ -33,7 +33,7 @@ jobs:
       - name: Coveralls GitHub Action
         uses: coverallsapp/github-action@v2.3.6
         with:
-          github-token: ${{ secrets.COVERALLS_REPO_TOKEN }}
+          github-token: ${{ secrets.GITHUB_TOKEN }}
 
   docs:
     runs-on: ubuntu-latest