fix: wrong default TimeFormat

[ionling]

The default timezone is 2006-01-02 15:04:05 UTC not 2006-01-02 15:04:05 Z0700.
Just fixed it.

[codecov-commenter]

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Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 98.71%. Comparing base (eef3a25) to head (c036406).
Report is 41 commits behind head on main.

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Additional details and impacted files

@@            Coverage Diff             @@
##             main     #549      +/-   ##
==========================================
- Coverage   98.80%   98.71%   -0.09%     
==========================================
  Files          85       85              
  Lines        5867     5858       -9     
==========================================
- Hits         5797     5783      -14     
- Misses         51       56       +5     
  Partials       19       19              

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