Fix periodic async callbacks

[philippjfr]

Fixes #5986

[codecov]

Codecov Report

Attention: 1 lines in your changes are missing coverage. Please review.

Comparison is base (46ea554) 84.61% compared to head (56b8af7) 84.69%.
Report is 1 commits behind head on main.

Files	Patch %	Lines
panel/io/callbacks.py	83.33%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #6053      +/-   ##
==========================================
+ Coverage   84.61%   84.69%   +0.08%     
==========================================
  Files         295      295              
  Lines       43936    43949      +13     
==========================================
+ Hits        37175    37224      +49     
+ Misses       6761     6725      -36     

Flag	Coverage Δ
ui-tests	40.66% <17.64%> (-0.01%)	⬇️
unitexamples-tests	72.83% <94.11%> (+0.12%)	⬆️

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