Fix server-side Tabulator selection changes

[philippjfr]

Currently resetting a selection in a server side callback does not work.

[codecov]

Codecov Report

Merging #2252 (01f1168) into master (6a0c8c8) will decrease coverage by 0.01%.
The diff coverage is 0.00%.

@@            Coverage Diff             @@
##           master    #2252      +/-   ##
==========================================
- Coverage   83.65%   83.63%   -0.02%     
==========================================
  Files         183      183              
  Lines       21900    21899       -1     
==========================================
- Hits        18320    18316       -4     
- Misses       3580     3583       +3     

Impacted Files	Coverage Δ
panel/widgets/tables.py	84.07% <0.00%> (-0.19%)	⬇️
panel/io/reload.py	64.36% <0.00%> (-2.30%)	⬇️

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