Correctly prepare coverage before codecov upload.

The new codecov uploader strictly does upload, and none of the magic
preparation that that bash uploader did. So we need to make sure we have
a full coverage XML report to upload.

Author: QuLogic

.github/workflows/tests.yml

@@ -219,7 +219,7 @@ jobs:
         run: |
           ${{ matrix.XVFB_RUN }} python -mpytest -raR -n auto \
             --maxfail=50 --timeout=300 --durations=25 \
-            --cov-report= --cov=lib --log-level=DEBUG
+            --cov-report=xml --cov=lib --log-level=DEBUG
 
       - name: Filter C coverage
         run: |