Update ipywidgets for compatibility with latest bokeh

[philippjfr]

Fixes #2691
Fixes #1858 (patches font-awesome onto the widget)
Fixes #2353

[codecov]

Codecov Report

Merging #3299 (a766e80) into master (d7a6b66) will decrease coverage by 0.06%.
The diff coverage is 0.00%.

@@            Coverage Diff             @@
##           master    #3299      +/-   ##
==========================================
- Coverage   83.44%   83.38%   -0.07%     
==========================================
  Files         195      195              
  Lines       26451    26471      +20     
==========================================
  Hits        22072    22072              
- Misses       4379     4399      +20     

Impacted Files	Coverage Δ
panel/io/ipywidget.py	0.00% <0.00%> (ø)
panel/pane/ipywidget.py	50.00% <0.00%> (-1.36%)	⬇️
panel/pane/plot.py	58.37% <0.00%> (-1.21%)	⬇️

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