fix(eslint-plugin): [non-nullable-type-assertion-style] handle const assertion

[yeonjuan]

fixes #2879

[typescript-eslint]

Thanks for the PR, @yeonjuan!

typescript-eslint is a 100% community driven project, and we are incredibly grateful that you are contributing to that community.

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 #2881 (b20ad2e) into master (d35a539) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master    #2881   +/-   ##
=======================================
  Coverage   92.77%   92.77%           
=======================================
  Files         310      310           
  Lines       10367    10373    +6     
  Branches     2934     2936    +2     
=======================================
+ Hits         9618     9624    +6     
  Misses        346      346           
  Partials      403      403           

Flag	Coverage Δ
unittest	92.77% <100.00%> (+<0.01%)	⬆️

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

Impacted Files	Coverage Δ
...gin/src/rules/non-nullable-type-assertion-style.ts	100.00% <100.00%> (ø)

[bradzacher]

ezpz - LGTM - thanks for fixing this!