CI: fix Tox/multi-environment Codecov uploads

Author: akx

.github/workflows/test.yml

@@ -28,4 +28,8 @@ jobs:
         python -m pip install tox tox-gh-actions==2.1.0
     - name: Run test via Tox
       run: tox --skip-missing-interpreters
-    - uses: codecov/codecov-action@v1
+      env:
+        COVERAGE_XML_PATH: ${{ runner.temp }}
+    - uses: codecov/codecov-action@v2
+      with:
+        directory: ${{ runner.temp }}

tox.ini

@@ -13,7 +13,7 @@ deps =
 whitelist_externals = make
 commands = make clean-cldr test
 setenv =
-    PYTEST_FLAGS=--cov=babel
+    PYTEST_FLAGS=--cov=babel --cov-report=xml:{env:COVERAGE_XML_PATH:.coverage_cache}/coverage.{envname}.xml
 passenv =
     BABEL_*
     PYTEST_*