Bump django-cors-headers from 4.7.0 to 4.9.0 in /backend (#1974)

Bumps [django-cors-headers](https://github.com/adamchainz/django-cors-headers) from 4.7.0 to 4.9.0.
- [Changelog](https://github.com/adamchainz/django-cors-headers/blob/main/CHANGELOG.rst)
- [Commits](adamchainz/django-cors-headers@4.7.0...4.9.0)

---
updated-dependencies:
- dependency-name: django-cors-headers
  dependency-version: 4.9.0
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <[email protected]>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]