CI: fix codecov again (#9007)

Finally, the xml format was required (the sqlite format did work on the other PR for some reason man_shrugging, but xml is the recommended). Found this in their example at https://github.com/codecov/example-python/blob/master/.circleci/config.yml

.circleci/config.yml

@@ -20,8 +20,7 @@ jobs:
       - run: git submodule update --init
       - run: pip install --user tox
       - run: tox -e py38
-      - codecov/upload:
-          file: .coverage
+      - codecov/upload
 
   tests-embedapi:
     docker:

tox.ini

@@ -20,11 +20,11 @@ basepython =
 commands =
     /bin/sh -c '\
         export DJANGO_SETTINGS_MODULE=readthedocs.settings.test; \
-        pytest --cov-report= --cov-config .coveragerc --cov=. --pyargs readthedocs --suppress-no-test-exit-code -m "not proxito and not embed_api" {posargs:{env:TOX_POSARGS:-m "not search and not proxito and not embed_api"}}'
+        pytest --cov-report=xml --cov-config .coveragerc --cov=. --pyargs readthedocs --suppress-no-test-exit-code -m "not proxito and not embed_api" {posargs:{env:TOX_POSARGS:-m "not search and not proxito and not embed_api"}}'
 
     /bin/sh -c '\
         export DJANGO_SETTINGS_MODULE=readthedocs.settings.proxito.test; \
-        pytest --cov-report= --cov-config .coveragerc --cov=. --cov-append --pyargs readthedocs -m proxito --suppress-no-test-exit-code {posargs}'
+        pytest --cov-report=xml --cov-config .coveragerc --cov=. --cov-append --pyargs readthedocs -m proxito --suppress-no-test-exit-code {posargs}'
 
 [testenv:docs]
 description = Build readthedocs user documentation