Update codecov/codecov-action 7.0.0 to fix failing CI (#503)

6.0.1 tries to download a GPG key from a missing keybase account,
causing our CI actions to fail when they try to upload the coverage
report.

See: codecov/wrapper#75

Author: owtaylor

.github/workflows/ci.yml

@@ -128,7 +128,7 @@ jobs:
         run: uv run --locked pytest --cov-report=xml
 
       - name: Upload coverage report
-        uses: codecov/codecov-action@v6.0.1
+        uses: codecov/codecov-action@v7.0.0
         with:
           env_vars: OS,PYTHON
           disable_search: true