Make inline error behaviour consistent

[jotaen4tinypilot]

This is a super tiny UI detail I noticed while testing https://github.com/tiny-pilot/tinypilot-pro/pull/275, and I only wanted to keep track of it.

We have a unified <inline-message> now (which is super cool), but the behaviour is slightly inconsistent:

• E.g., on the login page, the inline error goes away as soon as you change the copy in the input field
• E.g., in the hostname dialog, the inline message stays there until you click “Apply and Restart” again

I personally like the second pattern better, because only because the user starts typing again doesn’t necessarily mean they have understood the entire message.