refactor: Default to UTC when parsing dates without a known timezone

[edgarrmondragon]

Follow-on of #2613.

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📚 Documentation preview 📚: https://meltano-sdk--2619.org.readthedocs.build/en/2619/

[codspeed-hq]

CodSpeed Performance Report

Merging #2619 will not alter performance

_{Comparing edgarrmondragon/refactor/default-utc (03c8472) with main (b619b0d)}

Summary

✅ 6 untouched benchmarks

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 89.71%. Comparing base (b619b0d) to head (03c8472).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2619   +/-   ##
=======================================
  Coverage   89.71%   89.71%           
=======================================
  Files          58       58           
  Lines        4853     4853           
  Branches      948      948           
=======================================
  Hits         4354     4354           
  Misses        349      349           
  Partials      150      150           

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