[bugfix] Fix default datefmt for the perflog handlers

[vkarak]

Closes #3643.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 91.25%. Comparing base (79f0c55) to head (6969b94).
⚠️ Report is 2 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #3644      +/-   ##
==========================================
- Coverage   91.26%   91.25%   -0.02%     
==========================================
  Files          62       62              
  Lines       13591    13591              
==========================================
- Hits        12404    12402       -2     
- Misses       1187     1189       +2     

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[vkarak]

Oh, I realized I have done this PR against develop. I'd need to rebase it on master so as to make it to 4.9.3.