fix: upgrade @umbraco-cms/backoffice from 15.1.2 to 15.2.1

Snyk has created this PR to upgrade @umbraco-cms/backoffice from 15.1.2 to 15.2.1.

See this package in npm:
@umbraco-cms/backoffice

See this project in Snyk:
https://app.snyk.io/org/jcdcdev/project/68c3140b-c488-4260-bfb5-075adc2bb8f0?utm_source=github&utm_medium=referral&page=upgrade-pr

Author: snyk-bot