Fix: Focus loss when generation buttons enter disabled state

[ishitaj34]

What?

Part of #589

Why?

PR is necessary to retain visible focus indication when buttons enter disabled state during generation.

How?

Testing showed the primary user-facing issue in these cases was loss of visible focus indication during disabled states. Adding accessibleWhenDisabled preserves the visible focus indicator during generation.

• Adds the accessibleWhenDisabled prop so focus is not lost while the button goes into disabled mode during generation.

Use of AI Tools

Testing Instructions

• Alt Text Generation
  • Add an Image block and select an image.
  • Focus the "Generate Alt Text" button using keyboard navigation.
  • Trigger generation.
  • Verify focus is retained during generation.

Same for Excerpt and Featured Image generation.

Changelog Entry

Fixed - Focus loss when buttons enter disabled state during generation.

[github-actions]

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 73.18%. Comparing base (3624c91) to head (e63b506).

Additional details and impacted files

@@            Coverage Diff             @@
##             develop     #611   +/-   ##
==========================================
  Coverage      73.18%   73.18%           
  Complexity      1731     1731           
==========================================
  Files             85       85           
  Lines           7473     7473           
==========================================
  Hits            5469     5469           
  Misses          2004     2004           

Flag	Coverage Δ
unit	73.18% <ø> (ø)

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