Fix missing utf-8 decoding in tests

[philippjfr]

No description provided.

[codecov]

Codecov Report

Attention: Patch coverage is 62.50000% with 3 lines in your changes are missing coverage. Please review.

Project coverage is 40.16%. Comparing base (365bf37) to head (1ab1ea2).
Report is 2 commits behind head on main.

Files	Patch %	Lines
panel/pane/_textual.py	0.00%	2 Missing ⚠️
panel/tests/test_docs.py	0.00%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##             main    #6641       +/-   ##
===========================================
- Coverage   71.17%   40.16%   -31.01%     
===========================================
  Files         313      313               
  Lines       46133    46132        -1     
===========================================
- Hits        32834    18529    -14305     
- Misses      13299    27603    +14304     

Flag	Coverage Δ
ui-tests	39.99% <62.50%> (?)
unitexamples-tests	22.18% <0.00%> (-49.00%)	⬇️

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