fix(targets): Added a condition to the No schema for record field warning

[tobiascadee]

If schema flattening is enabled but a value for a key in the record which is flattened is None, this warning is returned because the record can not be flattened and then the key is not in the schema. This can be avoided by checking if the value is None. If it is None the record field actually does not exist so we do not need a warning.

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📚 Documentation preview 📚: https://meltano-sdk--2348.org.readthedocs.build/en/2348/

[codspeed-hq]

CodSpeed Performance Report

Merging #2348 will not alter performance

_{Comparing tobiascadee:tobias/fix/add-condition-to-no-schema-for-record-warning (a0fac04) with main (acb7487)}

Summary

✅ 6 untouched benchmarks

[codecov]

Codecov Report

Attention: Patch coverage is 50.00000% with 1 lines in your changes are missing coverage. Please review.

Project coverage is 88.74%. Comparing base (acb7487) to head (a0fac04).
Report is 4 commits behind head on main.

Files	Patch %	Lines
singer_sdk/sinks/core.py	50.00%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2348      +/-   ##
==========================================
- Coverage   88.76%   88.74%   -0.02%     
==========================================
  Files          54       54              
  Lines        4771     4772       +1     
  Branches      928      929       +1     
==========================================
  Hits         4235     4235              
  Misses        374      374              
- Partials      162      163       +1     

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[edgarrmondragon]

Thanks @tobiascadee!