Unpin jupyterlite-core version

[philippjfr]

Attempt at fixing tests by unpinning jupyterlite-core.

[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 (752626d) to head (4bbe502).
Report is 4 commits behind head on main.

Files	Patch %	Lines
panel/tests/ui/io/test_jupyterlite.py	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #7129      +/-   ##
==========================================
+ Coverage   72.38%   82.24%   +9.85%     
==========================================
  Files         326      327       +1     
  Lines       48824    48828       +4     
==========================================
+ Hits        35343    40158    +4815     
+ Misses      13481     8670    -4811     

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