chore(deps): update Cocoa SDK to v9.21.0

[github-actions]

Bumps modules/sentry-cocoa from 9.20.0 to 9.21.0.

Auto-generated by a dependency updater.

Changelog

Commits between 9.20.0 and 9.21.0

• release: 9.21.0
• fix: reorder an import since the linting rules changed right after this merged (#8370)
• lint: group imports by attribute (#8366)
• feat: add build flags + targets for enabling a KSCrash Integration (#8154)
• chore: Cancel pending saucelabs jobs (#8362)
• ci: skip simulator resolution in build-only and lint jobs (#8349)
• ci: cache Homebrew and skip auto-update in CI (#8354)
• chore: Remove sample app macOS deployment target (#8329)
• ci: Add file filter to Xcode 27 workflow (#8347)
• feat: Add feature flag scope ObjC API (#8160)
• feat: Attach feature flag evaluations to active spans (#8158)
• chore(ci): Skip rbenv install if ruby version is cached (#8350)
• chore: Align deinit handler of hang and runloop delay tracker (#8352)
• fix: snapshot currentHub under currentHubLock in span, startProfiler, stopProfiler (#8318)
• Merge branch 'release/9.20.0'
• ci: publish junit report on re-runs (#8344)

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 74.20%. Comparing base (1048afa) to head (89c60db).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5359      +/-   ##
==========================================
+ Coverage   74.19%   74.20%   +0.01%     
==========================================
  Files         509      509              
  Lines       18386    18386              
  Branches     3600     3600              
==========================================
+ Hits        13642    13644       +2     
+ Misses       3870     3869       -1     
+ Partials      874      873       -1     

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[jamescrosswell]

Automated approval: dependency update, CI green, no breaking changes in description.