Add behaviour to always use datetime.UTC if there is no zoneinfo available

[Miauwkeru]

DIS-2238

[codecov[bot]]

Codecov Report

Merging #86 (4a69b7f) into main (2e2eb62) will decrease coverage by 0.05%. The diff coverage is 60.00%.

@@            Coverage Diff             @@
##             main      #86      +/-   ##
==========================================
- Coverage   79.27%   79.22%   -0.05%     
==========================================
  Files          32       32              
  Lines        2924     2932       +8     
==========================================
+ Hits         2318     2323       +5     
- Misses        606      609       +3     

Flag	Coverage Δ
unittests	79.22% <60.00%> (-0.05%)	:arrow_down:

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Files	Coverage Δ
flow/record/fieldtypes/__init__.py	91.40% <60.00%> (-0.77%)	:arrow_down:

... and 1 file with indirect coverage changes

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[yunzheng]

LGTM