chore(deps): bump ical-generator from 9.0.0 to 11.0.0 in /backend

Bumps [ical-generator](https://github.com/sebbo2002/ical-generator) from 9.0.0 to 11.0.0.
- [Release notes](https://github.com/sebbo2002/ical-generator/releases)
- [Changelog](https://github.com/sebbo2002/ical-generator/blob/develop/CHANGELOG.md)
- [Commits](sebbo2002/ical-generator@v9.0.0...v11.0.0)

---
updated-dependencies:
- dependency-name: ical-generator
  dependency-version: 11.0.0
  dependency-type: direct:production
  update-type: version-update:semver-major
...

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

Author: dependabot[bot]

backend/package-lock.json

@@ -56,7 +56,7 @@
     "express-rate-limit": "^8.4.1",
     "google-auth-library": "^10.6.2",
     "googleapis": "^171.4.0",
-    "ical-generator": "^9.0.0",
+    "ical-generator": "^11.0.0",
     "jsonwebtoken": "^9.0.3",
     "multer": "^2.1.1",
     "node-cron": "^4.2.1",