fix(eslint-plugin): do not use .at(), Node 14 does not support it

[coyotte508]

PR Checklist

• Addresses an existing open issue: fixes Bug: [key-spacing] Crashes on Node 14 #6396
• That issue was marked as accepting prs
• Steps in Contributing were taken

Overview

[typescript-eslint]

Thanks for the PR, @coyotte508!

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 #6402 (9b91293) into main (fbe811c) will increase coverage by 0.00%.
The diff coverage is 100.00%.

❗ Current head 9b91293 differs from pull request most recent head f222453. Consider uploading reports for the commit f222453 to get more accurate results

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #6402   +/-   ##
=======================================
  Coverage   91.38%   91.38%           
=======================================
  Files         368      368           
  Lines       12605    12608    +3     
  Branches     3712     3713    +1     
=======================================
+ Hits        11519    11522    +3     
  Misses        770      770           
  Partials      316      316           

Flag	Coverage Δ
unittest	91.38% <100.00%> (+<0.01%)	⬆️

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

Impacted Files	Coverage Δ
packages/eslint-plugin/src/rules/key-spacing.ts	99.29% <100.00%> (+0.01%)	⬆️

[JoshuaKGoldberg]

Thanks!