fix: upgrade @umbraco-cms/backoffice from 16.3.3 to 16.4.0

Snyk has created this PR to upgrade @umbraco-cms/backoffice from 16.3.3 to 16.4.0.

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

See this project in Snyk:
https://app.snyk.io/org/jcdcdev/project/75226e0e-11c9-4207-9d37-c10025a42b1e?utm_source=github&utm_medium=referral&page=upgrade-pr

Author: snyk-bot