Fix crash of the dump tool

[mrbean-bremen]

• this was a regression due to incomplete refactoring

Also fixed a deprecation warning.

[codecov-commenter]

Codecov Report

Attention: 1 lines in your changes are missing coverage. Please review.

Comparison is base (4b23b82) 89.66% compared to head (507c5e4) 89.69%.
Report is 1 commits behind head on main.

Files	Patch %	Lines
dicom_validator/dump_dcm_info.py	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #75      +/-   ##
==========================================
+ Coverage   89.66%   89.69%   +0.03%     
==========================================
  Files          15       15              
  Lines        1625     1630       +5     
==========================================
+ Hits         1457     1462       +5     
  Misses        168      168              

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