tree-wide: replace utcnow and utcfromtimestamp

[evverx]

They were deprecated in python/cpython#103857.

Closes #4460

[codecov]

Codecov Report

Attention: Patch coverage is 40.00000% with 6 lines in your changes missing coverage. Please review.

Project coverage is 81.49%. Comparing base (ed7225d) to head (c47b6cf).

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #4462      +/-   ##
==========================================
- Coverage   81.49%   81.49%   -0.01%     
==========================================
  Files         355      355              
  Lines       84643    84643              
==========================================
- Hits        68983    68980       -3     
- Misses      15660    15663       +3     

Files	Coverage Δ
scapy/layers/http.py	83.53% <100.00%> (ø)
scapy/__init__.py	83.78% <50.00%> (ø)
scapy/modules/ticketer.py	35.66% <0.00%> (ø)
scapy/layers/kerberos.py	67.43% <33.33%> (ø)

... and 3 files with indirect coverage changes

[gpotter2]

This looks good, thanks a lot for looking into it.