Use regular ".now" instead of ".utcnow" with UTC zone

[yarikoptic]

It is mandated by starting to receive a DeprecationWarning in python 3.12

DeprecationWarning: datetime.datetime.utcnow() is deprecated and scheduled for removal in a future version. Use timezone-aware objects to represent datetimes in UTC: datetime.datetime.now(datetime.UTC)

discovered while addressing some other rot in heudiconv.

[codecov]

Codecov Report

Attention: Patch coverage is 91.66667% with 1 line in your changes missing coverage. Please review.

Project coverage is 39.50%. Comparing base (4d1352a) to head (fce346e).

Files with missing lines	Patch %	Lines
nipype/pipeline/engine/workflows.py	50.00%	1 Missing ⚠️

❗ There is a different number of reports uploaded between BASE (4d1352a) and HEAD (fce346e). Click for more details.

HEAD has 69 uploads less than BASE

Flag	BASE (4d1352a)	HEAD (fce346e)
	73	4

Additional details and impacted files

@@             Coverage Diff             @@
##           master    #3670       +/-   ##
===========================================
- Coverage   70.83%   39.50%   -31.33%     
===========================================
  Files        1276     1277        +1     
  Lines       59314    59322        +8     
  Branches     9824     9825        +1     
===========================================
- Hits        42013    23435    -18578     
- Misses      16125    35729    +19604     
+ Partials     1176      158     -1018     

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[yarikoptic]

eh, it isn't in 3.8 yet, so we have to craft python version specific adapter ...

now fails some other unrelated tests so must be something else (should be string instead of bytes?)

=========================== short test summary info ============================
FAILED algorithms/tests/test_CompCor.py::TestCompCor::test_compcor - ValueError: invalid fmt: b'%.10f'
FAILED algorithms/tests/test_CompCor.py::TestCompCor::test_compcor_variance_threshold_and_metadata - ValueError: invalid fmt: b'%.10f'
FAILED algorithms/tests/test_CompCor.py::TestCompCor::test_tcompcor - ValueError: invalid fmt: b'%.10f'
FAILED algorithms/tests/test_CompCor.py::TestCompCor::test_tcompcor_no_percentile - ValueError: invalid fmt: b'%.10f'
FAILED algorithms/tests/test_CompCor.py::TestCompCor::test_compcor_no_regress_poly - ValueError: invalid fmt: b'%.10f'
FAILED algorithms/tests/test_CompCor.py::TestCompCor::test_tcompcor_asymmetric_dim - ValueError: invalid fmt: b'%.10f'
FAILED algorithms/tests/test_CompCor.py::TestCompCor::test_tcompcor_merge_intersect_masks - ValueError: invalid fmt: b'%.10f'
FAILED algorithms/tests/test_CompCor.py::TestCompCor::test_tcompcor_index_mask - ValueError: invalid fmt: b'%.10f'
FAILED interfaces/cmtk/cmtk.py::nipype.interfaces.cmtk.cmtk.length
FAILED interfaces/mixins/fixheader.py::nipype.interfaces.mixins.fixheader.CopyHeaderInterface
= 10 failed, 2724 passed, 243 skipped, 5 xfailed, 48 warnings in 142.18s (0:02:22) =