test: fix coverage CI action (#94)

This commit fixes the coverage CI action to use the proper Django version to ensure that it runs successfully in CI.

.github/workflows/ci.yml

@@ -37,7 +37,7 @@ jobs:
       run: tox
 
     - name: Run coverage
-      if: matrix.python-version == '3.8' && matrix.toxenv == 'django40'
+      if: matrix.python-version == '3.8' && matrix.toxenv == 'django42'
       uses: py-cov-action/python-coverage-comment-action@v3
       with:
         GITHUB_TOKEN: ${{ github.token }}