Bump codecov/codecov-action from 3 to 4

Bumps [codecov/codecov-action](https://github.com/codecov/codecov-action) from 3 to 4.
- [Release notes](https://github.com/codecov/codecov-action/releases)
- [Changelog](https://github.com/codecov/codecov-action/blob/main/CHANGELOG.md)
- [Commits](codecov/codecov-action@v3...v4)

---
updated-dependencies:
- dependency-name: codecov/codecov-action
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <support@github.com>

Also added Codecov token, as token-less uploading is unsupported from v4
- see https://github.com/codecov/codecov-action/blob/main/CHANGELOG.md#400-beta1.

Co-authored-by: Anders <6058745+ddabble@users.noreply.github.com>

.github/workflows/test.yml

@@ -83,8 +83,9 @@ jobs:
           DJANGO: ${{ matrix.django-version }}
 
       - name: Upload coverage
-        uses: codecov/codecov-action@v3
+        uses: codecov/codecov-action@v4
         with:
+          token: ${{ secrets.CODECOV_TOKEN }}
           name: Python ${{ matrix.python-version }}, Django ${{ matrix.django-version }}