Use Python codecov package instead of GH action

We can't set the working directory of the GH Action which means we need
to install codecov ourselves and run it in the `tests/` sub-directory.

Author: betatim

.github/workflows/test.yml

@@ -117,8 +117,7 @@ jobs:
           cd tests
           pytest --durations 10 --cov repo2docker -v ${{ matrix.repo_type }}
 
-      # Action Repo: https://github.com/codecov/codecov-action
-      - uses: codecov/codecov-action@v1
-        working-directory: ./tests
-        with:
-          directory: ./tests
+      - name: "Upload code coverage stats"
+        run: |
+          pip install codecov
+          pushd tests && codecov && popd