Add compatibility for latest Textual

[philippjfr]

Fixes #7117

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 4 lines in your changes missing coverage. Please review.

Project coverage is 72.37%. Comparing base (752626d) to head (b6e8092).
Report is 1 commits behind head on main.

Files	Patch %	Lines
panel/pane/_textual.py	0.00%	4 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #7130      +/-   ##
==========================================
- Coverage   72.38%   72.37%   -0.01%     
==========================================
  Files         326      326              
  Lines       48824    48827       +3     
==========================================
- Hits        35342    35340       -2     
- Misses      13482    13487       +5     

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