Add selective Codecov submit

Only for Linux, only for ready PRs, and only for PRs to `main` or
`stable`.

.github/workflows/all_core_tests.yml

@@ -40,3 +40,10 @@ jobs:
     - name: Run tests & report source coverage
       run: |
         pytest --cov --testall --nonloc
+
+    - name: Submit to Codecov if Linux and ready status
+      if: ${{ matrix.os == 'ubuntu-latest' && !github.event.pull_request.draft && (github.event.pull_request.base.ref == 'main' || github.event.pull_request.base.ref == 'stable') }}
+      run: |
+        curl -Os https://cli.codecov.io/latest/linux/codecov
+        chmod +x codecov
+        ./codecov --verbose upload-process --fail-on-error -t ${{ secrets.CODECOV_TOKEN }} -n 'service'-${{ github.run_id }} -F service -f coverage-service.xml