[ci] Fix description of custom checkout action

[ricab]

The action claimed it checked out Multipass code, but that is actually
done elsewhere via the standard GitHub "checkout" action.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 89.44%. Comparing base (f7ba74f) to head (a3ef9e4).
Report is 183 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3996      +/-   ##
==========================================
+ Coverage   89.27%   89.44%   +0.17%     
==========================================
  Files         259      260       +1     
  Lines       14653    14999     +346     
==========================================
+ Hits        13081    13416     +335     
- Misses       1572     1583      +11     

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[ricab]

I don't have any further fixes at this point, so may as well merge.

[Copilot]

Copilot reviewed 1 out of 1 changed files in this pull request and generated no comments.

Comments suppressed due to low confidence (1)

.github/actions/checkout/action.yml:2

• Consider explicitly mentioning that the checkout of the Multipass code is handled by the standard GitHub checkout action to avoid any confusion.

description: Get tags and submodules for the Multipass repository

[Sploder12]

Yep, that's more accurate!