Fix menu buttons in issues and release (#30056)

Fix menu buttons in issues and release (#30056)

Fix regression from https://github.com/go-gitea/gitea/pull/30033

These buttons had lost their border because `.ui.header` sets `none` but
`.ui.menu` has it, after the migration, the order of styles changed and
header won. I see no reason why those have the `header` class in first
place, besides for semantic meaning.

Before:
<img width="491" alt="Screenshot 2024-03-25 at 00 39 27"
src="https://github.com/go-gitea/gitea/assets/115237/fa1b7505-75cf-4854-a97f-db3c46f31e93">

After:
<img width="496" alt="Screenshot 2024-03-25 at 00 39 14"
src="https://github.com/go-gitea/gitea/assets/115237/8f6bdc07-9596-436b-8c82-9af283300004">