Ensure user cookie can be unencoded

[philippjfr]

Fixes #6898

[codecov]

Codecov Report

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

Project coverage is 72.29%. Comparing base (4e351ed) to head (d406381).

Files	Patch %	Lines
panel/io/application.py	0.00%	4 Missing ⚠️

❗ There is a different number of reports uploaded between BASE (4e351ed) and HEAD (d406381). Click for more details.

HEAD has 4 uploads less than BASE

| Flag | BASE (4e351ed) | HEAD (d406381) | |------|------|------| ||8|4|

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #6937      +/-   ##
==========================================
- Coverage   81.16%   72.29%   -8.88%     
==========================================
  Files         323      322       -1     
  Lines       47626    47628       +2     
==========================================
- Hits        38658    34432    -4226     
- Misses       8968    13196    +4228     

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