Rename check_permission() to check_permissions() on WP_Ability

[gziolo]

Follow up for #76.
Closes #67.

Addresses feedback from @justlevine:

• https://github.com/WordPress/abilities-api/pull/76/files#r2384356477
• https://github.com/WordPress/abilities-api/pull/76/files#r2384359503
• https://github.com/WordPress/abilities-api/pull/76/files#r2384360545
• Fix has_permission() return type inconsistency (Issue #67) #76 (comment)

I'm sorry to be pedantic, but as #76 (comment) the REST API uses check_{_}permissions() plural, even though the registry arg is permission_callback. It's also more grammatically accurate when paired with the verb check.

[github-actions]

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

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 85.69%. Comparing base (8e0b08a) to head (99824fa).
⚠️ Report is 1 commits behind head on trunk.

Additional details and impacted files

@@            Coverage Diff            @@
##              trunk      #94   +/-   ##
=========================================
  Coverage     85.69%   85.69%           
  Complexity      103      103           
=========================================
  Files            16       16           
  Lines           776      776           
  Branches         86       86           
=========================================
  Hits            665      665           
  Misses          111      111           

Flag	Coverage Δ
javascript	92.66% <ø> (ø)
unit	82.97% <100.00%> (ø)

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[justlevine]

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