chore(deps): bump icalendar from 4.0.7 to 6.0.0

Bumps [icalendar](https://github.com/collective/icalendar) from 4.0.7 to 6.0.0.
- [Release notes](https://github.com/collective/icalendar/releases)
- [Changelog](https://github.com/collective/icalendar/blob/main/CHANGES.rst)
- [Commits](collective/icalendar@4.0.7...v6.0.0)

---
updated-dependencies:
- dependency-name: icalendar
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <[email protected]>

base-requirements.txt

@@ -17,7 +17,7 @@ lxml==5.2.2
 cssselect==1.2.0
 feedparser==6.0.11
 beautifulsoup4==4.12.3
-icalendar==4.0.7
+icalendar==6.0.0
 chardet==4.0.0
 celery[redis]==5.4.0
 django-celery-beat==2.5.0