Enable include-hidden-files option for coverage upload

This resolves an issue where the `.coverage.{python_version}` file was not
uploaded.

See actions/upload-artifact#602 and
https://hypothes-is.slack.com/archives/C4K6M7P5E/p1725285976308269.

.github/workflows/ci.yml

@@ -101,6 +101,7 @@ jobs:
         with:
           name: coverage
           path: .coverage.*
+          include-hidden-files: true
   Coverage:
     needs: tests
     runs-on: ubuntu-latest