Fix Win TZ bug

[uckelman-sf]

[simsong]

I've done some research on the handling of TZ under mingw. Apparently the variable sometimes ignored, depending on which C runtime is being used. Setting TZ before the program runs sometimes works, but changing it when the program is running mostly does not unless _tzset() is called.

I've created some tests for this here: https://github.com/sleuthkit/sleuthkit/pull/3351/files#diff-8c1bfabcdffc6a7f7fc6510c6fe2b9457aa53a921b159481cb4eb6bd53a843d4

[codecov[bot]]

Codecov Report

:white_check_mark: All modified and coverable lines are covered by tests. :white_check_mark: Project coverage is 27.57%. Comparing base (df1bc00) to head (08afb30).

Additional details and impacted files

@@           Coverage Diff            @@
##           develop    #3045   +/-   ##
========================================
  Coverage    27.56%   27.57%           
========================================
  Files          220      220           
  Lines        45782    45782           
  Branches      7462     7462           
========================================
+ Hits         12619    12621    +2     
+ Misses       33163    33161    -2     

Flag	Coverage Δ
unittests	27.57% <ø> (+<0.01%)	:arrow_up:

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[simsong]

I'm moving this from draft to ready status, cleaned up the comment history, and will be accepting this after review by ChatGPT.