Update showcase image-generation webp asset

[simison]

Replace the previous showcase-image-generation.webp with a new asset.

What?

Follow-up from #505 (comment)

Why?

How?

Used this to convert from png to webp

brew install webp

cwebp -q 90 -alpha_q 85 -m 6 -resize 1260 0 \
  assets/images/showcase-image-generation.png \
  -o assets/images/showcase-image-generation.webp

Use of AI Tools

Yes

Testing Instructions

Screenshots or screencast

Before

After

Changelog Entry

Added - New feature.
Changed - Existing functionality.
Deprecated - Soon-to-be removed feature.
Removed - Feature.
Fixed - Bug fix.
Security - Vulnerability.
Developer - Development related updates.

[github-actions]

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Co-authored-by: simison <simison@git.wordpress.org>

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 67.25%. Comparing base (4736d6f) to head (749aea8).

Additional details and impacted files

@@              Coverage Diff              @@
##             develop     #519      +/-   ##
=============================================
+ Coverage      67.23%   67.25%   +0.01%     
  Complexity      1054     1054              
=============================================
  Files             65       65              
  Lines           5024     5024              
=============================================
+ Hits            3378     3379       +1     
+ Misses          1646     1645       -1     

Flag	Coverage Δ
unit	67.25% <ø> (+0.01%)	⬆️

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