fix(AdminSettings): server buttons visual interactivity

[ShGKme]

☑️ Resolves

• A part of: Adjust UI according to the design review #12800

🖌️ UI Checklist

🖼️ Screenshots / Screencasts

🏚️ Before	🏡 After

🚧 Tasks

• Replace tertiary-no-background -> tertiary
  • Recording server - delete
  • Signaling server - delete
  • STUN server - delete (+ add a missing gap here)
  • TURN server - delete + test.
• Prevent infinite loading in TURN server testing
  • Don't switch to "testing" (loading) state if testing is not happening
    
  • Disable the testing button when testing is not possible
    
• Align turn settings on center to avoid button stretch

  Before	After

🏁 Checklist

• 🌏 Tested with Chrome, Firefox and Safari or should not be risky to browser differences
• 🖥️ Tested with Desktop client or should not be risky for it
• 🖌️ Design was reviewed, approved or inspired by the design team
• ⛑️ Tests are included or not possible
• 📗 User documentation in https://github.com/nextcloud/documentation/tree/master/user_manual/talk has been updated or is not required

[ShGKme]

• Rebased onto main
• Fixed button stretch issue