build(deps): bump icalendar from 5.0.12 to 5.0.13

Bumps [icalendar](https://github.com/collective/icalendar) from 5.0.12 to 5.0.13.
- [Release notes](https://github.com/collective/icalendar/releases)
- [Changelog](https://github.com/collective/icalendar/blob/main/CHANGES.rst)
- [Commits](collective/icalendar@v5.0.12...v5.0.13)

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

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

requirements.txt

@@ -1 +1 @@
-icalendar==5.0.12
+icalendar==5.0.13