Reuse the same translation keystrings for the same labels in milestone dropdown menus

[SimonPistache]

Description

I noticed the Milestone dropdown selector used in the sidebar of an issue/PR doesn't use the same translation keystring as the ones used in the filters and actions menubars

Keystring used in the sidebar

Keystring used in the actionbar & filterbar

---

Further more, the actions menubars misuses the 'open' keystring for both opened and closed milestones, whereas it should use the 'close' keystring.

Screenshots

Gitea Version

1.22.3

Can you reproduce the bug on the Gitea demo site?

Yes

Operating System

Macos

Browser Version

Firefox 132

[SimonPistache]

Suggested changes:

• Fix the off-label about closed milestones on the actionbar dropdown
• Change keystrings used in the sidebar to reuse the ones used in the actionbar and the filterbar
• Remove the now unused keystrings (idk how crowdin handle keystring deletions in the code)