Update alt text loading state

[jeffpaul]

Description

Let's update the loading button style from the existing:

alt-text-loading-state.mp4

to match our otherwise standard loading state (without the arrow bits inside the button):

Step-by-step reproduction instructions

.

Screenshots, screen recording, code snippet

No response

Environment info

No response

Please confirm that you have searched existing issues in the repo.

• Yes

Please confirm that you have tested with all plugins deactivated except the AI plugin.

• Yes

Please confirm which theme type you used for testing.

• Block
• Classic
• Hybrid (e.g. classic with theme.json)
• Not sure