Change type check when file is passed ar requirements for convert

[etihwo]

Update script_to_html fucntion when the convert command is called with a .txt file since the commit 7afcc90 converts the requirements variable with the function pathlib.Path() when it is a .txt file.

Fixes #7565

[codecov]

Codecov Report

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

Project coverage is 82.24%. Comparing base (d48c45f) to head (2e04569).

Files with missing lines	Patch %	Lines
panel/io/convert.py	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #7566      +/-   ##
==========================================
+ Coverage   82.23%   82.24%   +0.01%     
==========================================
  Files         339      339              
  Lines       51476    51476              
==========================================
+ Hits        42330    42337       +7     
+ Misses       9146     9139       -7     

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