Fix sidebar label dropdown divider (#25359)
Follow #25312
Also fix the label dropdown on sidebar
Before:
<img width="1345" alt="Screen Shot 2023-06-19 at 08 55 05"
src="https://github.com/go-gitea/gitea/assets/17645053/3a98e871-b482-4ecb-8ce2-74df67fb65a7">
After:
<img width="1408" alt="Screen Shot 2023-06-19 at 08 57 17"
src="https://github.com/go-gitea/gitea/assets/17645053/09af15cc-1250-49b3-98b6-5b1a2b9021cb">