fix: fixed filtering by unquoted logfmt predefined fields

[pamburus]

Closes #1052

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 88.64%. Comparing base (abe3568) to head (56a1685).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1053   +/-   ##
=======================================
  Coverage   88.64%   88.64%           
=======================================
  Files          47       47           
  Lines       13679    13681    +2     
=======================================
+ Hits        12126    12128    +2     
  Misses       1553     1553           

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