⬆️ Bump codecov/codecov-action from 3 to 4 (#869)

Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>
Co-authored-by: Chris Sewell <chrisj_sewell@hotmail.com>

Author: dependabot[bot]

.github/workflows/tests.yml

@@ -54,7 +54,7 @@ jobs:
         coverage xml
     - name: Upload to Codecov
       if: github.repository == 'executablebooks/MyST-Parser' && matrix.python-version == 3.8 && matrix.os == 'ubuntu-latest'
-      uses: codecov/codecov-action@v3
+      uses: codecov/codecov-action@v4
       with:
         token: ${{ secrets.CODECOV_TOKEN }}
         name: myst-parser-pytests