Fix Ace widget disabled parameter

[philippjfr]

Fixes #1808

[codecov]

Codecov Report

Merging #2449 (1c395fd) into master (a00392a) will increase coverage by 0.01%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #2449      +/-   ##
==========================================
+ Coverage   83.39%   83.40%   +0.01%     
==========================================
  Files         182      182              
  Lines       22739    22753      +14     
==========================================
+ Hits        18963    18977      +14     
  Misses       3776     3776              

Impacted Files	Coverage Δ
panel/widgets/ace.py	100.00% <100.00%> (ø)

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