Enable CodeCov CI

Author: aiudirog

.github/workflows/tests.yml

@@ -48,5 +48,5 @@ jobs:
           python -m pip install -U -r requirements.txt pytest-coverage codecov
       - name: Run Tests
         run: python -m pytest --cov=httpx_gssapi --cov-report=xml
-      # - name: Upload Coverage
-      # run: python -m codecov --token=${{ secrets.CODECOV_TOKEN }}
+      - name: Upload Coverage
+        run: python -m codecov --token=${{ secrets.CODECOV_TOKEN }}