Fix cache policy bug

[philippjfr]

Fixes #4785

[codecov]

Codecov Report

Merging #4789 (36b6094) into main (f351189) will decrease coverage by 0.57%.
The diff coverage is 80.00%.

@@            Coverage Diff             @@
##             main    #4789      +/-   ##
==========================================
- Coverage   83.37%   82.81%   -0.57%     
==========================================
  Files         268      268              
  Lines       37899    37901       +2     
==========================================
- Hits        31599    31387     -212     
- Misses       6300     6514     +214     

Flag	Coverage Δ
ui-tests	39.13% <20.00%> (-1.56%)	⬇️
unitexamples-tests	73.34% <80.00%> (+0.01%)	⬆️

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Impacted Files	Coverage Δ
panel/io/cache.py	84.45% <66.66%> (-0.30%)	⬇️
panel/tests/io/test_cache.py	97.12% <100.00%> (ø)

... and 7 files with indirect coverage changes

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