Fix programmatic updates to Tabulator page

[philippjfr]

Fixes #4517
Fixes #5186

[codecov]

Codecov Report

Merging #5187 (a3d0615) into main (209653e) will increase coverage by 9.78%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main    #5187      +/-   ##
==========================================
+ Coverage   73.77%   83.56%   +9.78%     
==========================================
  Files         274      274              
  Lines       39575    39583       +8     
==========================================
+ Hits        29198    33076    +3878     
+ Misses      10377     6507    -3870     

Flag	Coverage Δ
ui-tests	39.30% <100.00%> (?)
unitexamples-tests	73.77% <12.50%> (-0.01%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
panel/tests/ui/widgets/test_tabulator.py	99.32% <100.00%> (+89.89%)	⬆️

... and 53 files with indirect coverage changes

📣 We’re building smart automated test selection to slash your CI/CD build times. Learn more