fix(eslint-plugin): [no-unnecessary-type-assertion] correct bad fix for angle bracket assertion

[yeonjuan]

fixes #3196

[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!

---

🙏 Please, if you or your company is finding typescript-eslint valuable, help us sustain the project by sponsoring it transparently on https://opencollective.com/typescript-eslint. As a thank you, your profile/company logo will be added to our main README which receives thousands of unique visitors per day.

[codecov]

Codecov Report

Merging #3244 (ae9c141) into master (5414bf2) will decrease coverage by 0.01%.
The diff coverage is 60.00%.

@@            Coverage Diff             @@
##           master    #3244      +/-   ##
==========================================
- Coverage   92.93%   92.91%   -0.02%     
==========================================
  Files         316      316              
  Lines       10851    10854       +3     
  Branches     3067     3069       +2     
==========================================
+ Hits        10084    10085       +1     
  Misses        342      342              
- Partials      425      427       +2     

Flag	Coverage Δ
unittest	92.91% <60.00%> (-0.02%)	⬇️

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

Impacted Files	Coverage Δ
...-plugin/src/rules/no-unnecessary-type-assertion.ts	92.30% <60.00%> (-2.36%)	⬇️

[bradzacher]

thanks for doing this!