fix: `to_arrow` datetime conversion

[ianna]

fixes #3643

[github-actions[bot]]

The documentation preview is ready to be viewed at http://preview.awkward-array.org.s3-website.us-east-1.amazonaws.com/PR3647

[codecov[bot]]

Codecov Report

:x: Patch coverage is 50.00000% with 2 lines in your changes missing coverage. Please review. :white_check_mark: Project coverage is 82.70%. Comparing base (b749e49) to head (4398147). :warning: Report is 466 commits behind head on main.

Files with missing lines	Patch %	Lines
src/awkward/contents/numpyarray.py	50.00%	2 Missing :warning:

Additional details and impacted files

Files with missing lines	Coverage Δ
src/awkward/contents/numpyarray.py	91.07% <50.00%> (-0.44%)	:arrow_down:

... and 199 files with indirect coverage changes

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