Fixed FsObject error message to avoid recursion

[tclose]

when raising a FormatMismatchError, FsObject recursively attempts to print itself to a string

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 1 line in your changes missing coverage. Please review.

Project coverage is 92.44%. Comparing base (a9a3715) to head (81a652e).
Report is 14 commits behind head on main.

Files with missing lines	Patch %	Lines
fileformats/generic/fsobject.py	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #68      +/-   ##
==========================================
- Coverage   92.46%   92.44%   -0.02%     
==========================================
  Files          43       43              
  Lines        5041     5042       +1     
  Branches      553      554       +1     
==========================================
  Hits         4661     4661              
- Misses        286      287       +1     
  Partials       94       94              

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