Update PullRequest API assignees cannot be set to null #22140
Description
Description
We can't use the api to set assignees to empty，but you can do so on our web page.
Screenshots
use API
use web
Gitea Version
v1.19.0-dev
Can you reproduce the bug on the Gitea demo site?
Yes
Operating System
No response
Browser Version
Google Chrome 版本 103.0.5060.53（正式版本） (arm64)