ci: Report coverage for oldest and newest Python tested (#1817)

* Report coverage for the oldest Python (3.7) and newest (3.10) that are
tested to ensure that version specific 'if' statements are properly covered.
* Add Python version specific flags to the coverage reporting to compare
differences in coverage and track coverage changes across versions more easily.
* Follow up to PR #1753

.github/workflows/ci.yml

@@ -55,12 +55,16 @@ jobs:
       if: failure() && github.event_name == 'workflow_dispatch'
       uses: mxschmitt/action-tmate@v3
 
+      # Report coverage for oldest and newest Python tested to deal with version differences
     - name: Report core project coverage with Codecov
-      if: github.event_name != 'schedule' && matrix.python-version == '3.10' && matrix.os == 'ubuntu-latest'
+      if: >-
+        github.event_name != 'schedule' &&
+        (matrix.python-version == '3.7' || matrix.python-version == '3.10') &&
+        matrix.os == 'ubuntu-latest'
       uses: codecov/codecov-action@v2
       with:
         files: ./coverage.xml
-        flags: unittests
+        flags: unittests-${{ matrix.python-version }}
 
     - name: Test Contrib module with pytest
       run: |