ci,tox: generate coverage xml in tox, not in CI

This way CI doesn't need to install coverage on its own just to run the
`coverage report xml` command, instead it goes through tox.

Author: bluetech

.github/workflows/test.yml

@@ -271,7 +271,7 @@ jobs:
     - name: Install dependencies
       run: |
         python -m pip install --upgrade pip
-        pip install tox coverage
+        pip install tox
 
     - name: Test without coverage
       if: "! matrix.use_coverage"
@@ -283,10 +283,6 @@ jobs:
       shell: bash
       run: tox run -e ${{ matrix.tox_env }}-coverage --installpkg `find dist/*.tar.gz`
 
-    - name: Generate coverage report
-      if: "matrix.use_coverage"
-      run: python -m coverage xml
-
     - name: Upload coverage to Codecov
       if: "matrix.use_coverage"
       uses: codecov/codecov-action@5a1091511ad55cbe89839c7260b706298ca349f7

tox.ini

@@ -65,6 +65,8 @@ commands =
     doctesting: {env:_PYTEST_TOX_COVERAGE_RUN:} pytest --doctest-modules --pyargs _pytest
     coverage: coverage combine
     coverage: coverage report -m
+    # Run `coverage xml` only on CI.
+    coverage: python -c 'import os; os.environ.get("CI") and os.execlp("coverage", "coverage", "xml")'
 passenv =
     COVERAGE_*
     PYTEST_ADDOPTS