Bump caldav from 2.2.3 to 2.2.6

Bumps [caldav](https://github.com/python-caldav/caldav) from 2.2.3 to 2.2.6.
- [Release notes](https://github.com/python-caldav/caldav/releases)
- [Changelog](https://github.com/python-caldav/caldav/blob/master/CHANGELOG.md)
- [Commits](https://github.com/python-caldav/caldav/compare/v2.2.3...v2.2.6)

---
updated-dependencies:
- dependency-name: caldav
  dependency-version: 2.2.6
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

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

pyproject.toml

@@ -76,7 +76,7 @@ dependencies = [
         # User
         "drf-nested-routers",
         "vobject",
-        "caldav==2.2.3",
+        "caldav==2.2.6",
         # Amavis
         "html2text",
         "idna",