Invalidate layout on HTML re-rerender

[philippjfr]

Fixes #3609

[codecov]

Codecov Report

Merging #3616 (d254982) into master (923b253) will decrease coverage by 0.02%.
The diff coverage is 11.11%.

@@            Coverage Diff             @@
##           master    #3616      +/-   ##
==========================================
- Coverage   82.38%   82.36%   -0.03%     
==========================================
  Files         204      204              
  Lines       27855    27864       +9     
==========================================
+ Hits        22949    22950       +1     
- Misses       4906     4914       +8     

Impacted Files	Coverage Δ
panel/tests/ui/pane/test_markup.py	30.43% <11.11%> (-12.43%)	⬇️

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[MarcSkovMadsen]

Nice thanks.