fix(eslint-plugin): crash fixing readonly arrays to generic

[a-tarasyuk]

Fixes #1149

[typescript-eslint]

Thanks for the PR, @a-tarasyuk!

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The core maintainers work on this in their personal time, so please understand that it may not be possible for them to review your work immediately.

Thanks again!

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[codecov]

Codecov Report

Merging #1172 into master will increase coverage by 0.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master    #1172      +/-   ##
==========================================
+ Coverage   93.98%   93.99%   +0.01%     
==========================================
  Files         120      120              
  Lines        5185     5195      +10     
  Branches     1438     1440       +2     
==========================================
+ Hits         4873     4883      +10     
  Misses        178      178              
  Partials      134      134

Impacted Files	Coverage Δ
packages/eslint-plugin/src/rules/array-type.ts	93.33% <100%> (+0.7%)	⬆️

[bradzacher]

LGTM, thanks for this.