Bump icalendar from 5.0.7 to 6.1.0

Bumps [icalendar](https://github.com/collective/icalendar) from 5.0.7 to 6.1.0.
- [Release notes](https://github.com/collective/icalendar/releases)
- [Changelog](https://github.com/collective/icalendar/blob/main/CHANGES.rst)
- [Commits](collective/icalendar@v5.0.7...v6.1.0)

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

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

requirements/base.txt

@@ -12,7 +12,7 @@ djangorestframework==3.14.0
 django-redis==5.3.0
 hiredis==2.3.2
 redis==5.0.4
-icalendar==5.0.7
+icalendar==6.1.0
 dealer==2.1.0
 
 git+https://github.com/DemocracyClub/design-system.git@0.5.0