Replace deprecated imghdr

[penguinpee]

The module will be removed from Python 3.13:
https://docs.python.org/3.13/whatsnew/3.13.html#pep-594-dead-batteries-and-other-module-removals

[codecov]

Codecov Report

Attention: Patch coverage is 50.00000% with 1 line in your changes missing coverage. Please review.

Project coverage is 70.89%. Comparing base (ccec546) to head (303a0e8).
Report is 3 commits behind head on master.

Files with missing lines	Patch %	Lines
nipype/interfaces/dcmstack.py	50.00%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #3659   +/-   ##
=======================================
  Coverage   70.89%   70.89%           
=======================================
  Files        1277     1277           
  Lines       59212    59212           
  Branches     9799     9799           
=======================================
  Hits        41980    41980           
  Misses      16066    16066           
  Partials     1166     1166           

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