Removed old python3 container reference.

Author: simlist

.github/workflows/testing-and-coverage.yml

@@ -33,7 +33,6 @@ jobs:
     needs: test
     if: ${{ always() }}
     runs-on: ubuntu-latest
-    container: python:3-slim
     steps:
     - name: Coveralls Finished
       uses: coverallsapp/github-action@v2