Remove duplicate error display in generate Alt text

[juanfra]

What?

Removes the error message from the controls area when AI summary generation fails.

Why?

Errors were being displayed twice. Once in the top notice bar and again right above the button. This redundancy was confusing and you had to dismiss the two independently.

How?

Removed the error display from the controls area

Testing Instructions

1. Be sure that you don't have any AI provider with text generation capabilities configured (maybe just try without any configured)
2. Go to a page or post.
3. Add an image.
4. In the image controls, head over "Settings" and click "Generate Alt text"
5. Confirm the error notice is showing only once on the top bar.

Screenshots or screencast

Before

generate-alt-duplicated-error.mp4

After

[github-actions]

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Co-authored-by: jeffpaul <jeffpaul@git.wordpress.org>
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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 58.03%. Comparing base (f2b29e6) to head (6dbea05).
⚠️ Report is 17 commits behind head on develop.

Additional details and impacted files

@@            Coverage Diff             @@
##             develop     #255   +/-   ##
==========================================
  Coverage      58.03%   58.03%           
  Complexity       576      576           
==========================================
  Files             37       37           
  Lines           2955     2955           
==========================================
  Hits            1715     1715           
  Misses          1240     1240           

Flag	Coverage Δ
unit	58.03% <ø> (ø)

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[jeffpaul]

@karmatosed is there a standard approach within Gutenberg for this sort of error in terms of showing it at the top of the canvas or contextually within the sidebar? Which is the most optimal approach?

[jeffpaul]

@juanfra per input from @karmatosed in Slack, let's remove the error from the top of the canvas and keep the one in the sidebar.

[juanfra]

Thanks @jeffpaul! I shared my thoughts on that thread but maybe it's worth to centralize the conversation here.

I don't think we have a precedent for showing errors in the sidebar. If we set one here, it might mean revisiting how other experiments with sidebar controls handle errors too. Errors at the top feel more consistent with existing block editor patterns, and how we're doing it for the rest of the experiments. Happy to revisit if there are examples of this pattern elsewhere that I'm missing.

[jeffpaul]

@karmatosed can you confirm optional approach to align to how Gutenberg handles contextual error messages (feel free to ping Gutenberg designers/engineers to verify if needed)?

[gziolo]

can you confirm optional approach to align to how Gutenberg handles contextual error messages (feel free to ping Gutenberg designers/engineers to verify if needed)?

@jorgefilipecosta or @Mamaduka, what's the latest on showing errors in the UI: global snackbar (kept in this PR) or inline error notice (removed in this PR).

[Mamaduka]

As far as I know, we're still using snackbars for most cases. I think it will remain the same until normal notices are more flexible.

[gziolo]

Looks good. We can iterate when design recommendations change over time.