SDK-409: Prepare for Release 6.7.1

[github-actions]

Prepare for Release 6.7.1

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 https://github.com/Iterable/iterable-docs/pull/1481

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 70.77%. Comparing base (4cfef9c) to head (1802818).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1026      +/-   ##
==========================================
+ Coverage   70.76%   70.77%   +0.01%     
==========================================
  Files         112      112              
  Lines        9201     9201              
==========================================
+ Hits         6511     6512       +1     
+ Misses       2690     2689       -1     

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