SDK-209: Prepare for Release 6.6.4

[github-actions]

Prepare for Release 6.6.4

SDK Release Checklist

• CHANGELOG.md updated with correct version
• Version numbers updated:
  • Iterable-iOS-SDK.podspec
  • Iterable-iOS-AppExtensions.podspec
  • sdkVersion in IterableAPI.swift
• README.md reviewed (if needed)
• All tests passing
• Documentation updated (if needed)

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 69.41%. Comparing base (78fc9eb) to head (399d5cb).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #980   +/-   ##
=======================================
  Coverage   69.41%   69.41%           
=======================================
  Files         109      109           
  Lines        8917     8917           
=======================================
  Hits         6190     6190           
  Misses       2727     2727           

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