Patch ModelChangedEvents with array value

[philippjfr]

Temporary fix for #3456

[codecov]

Codecov Report

Merging #3460 (2f91741) into master (b0c1a21) will decrease coverage by 0.01%.
The diff coverage is 68.00%.

@@            Coverage Diff             @@
##           master    #3460      +/-   ##
==========================================
- Coverage   83.16%   83.14%   -0.02%     
==========================================
  Files         199      199              
  Lines       27061    27071      +10     
==========================================
+ Hits        22505    22508       +3     
- Misses       4556     4563       +7     

Impacted Files	Coverage Δ
panel/io/model.py	61.45% <64.70%> (+0.01%)	⬆️
panel/io/document.py	61.90% <75.00%> (+1.41%)	⬆️
panel/io/reload.py	69.56% <0.00%> (-2.18%)	⬇️
panel/tests/command/test_serve.py	83.54% <0.00%> (-1.46%)	⬇️
panel/io/server.py	78.04% <0.00%> (-0.22%)	⬇️
panel/io/state.py	70.38% <0.00%> (-0.22%)	⬇️
panel/pane/idom.py	27.40% <0.00%> (+0.20%)	⬆️
panel/io/callbacks.py	72.99% <0.00%> (+0.52%)	⬆️

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