docs: Add missing comma in CUSTOM_RULES.md

[zaicevas]

PR Checklist

• Addresses an existing issue: fixes #000
• That issue was marked as accepting prs
• Steps in CONTRIBUTING.md were taken

Overview

I think the PR title and content is self-explanatory

[nx-cloud]

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✅ Successfully ran 48 targets

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[typescript-eslint]

Thanks for the PR, @zaicevas!

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 #4464 (21c9ce1) into main (8894106) will increase coverage by 1.84%.
The diff coverage is n/a.

❗ Current head 21c9ce1 differs from pull request most recent head a4dc161. Consider uploading reports for the commit a4dc161 to get more accurate results

@@            Coverage Diff             @@
##             main    #4464      +/-   ##
==========================================
+ Coverage   92.70%   94.54%   +1.84%     
==========================================
  Files         183      147      -36     
  Lines        9759     7851    -1908     
  Branches     3054     2516     -538     
==========================================
- Hits         9047     7423    -1624     
+ Misses        480      234     -246     
+ Partials      232      194      -38     

Flag	Coverage Δ
unittest	94.54% <ø> (+1.84%)	⬆️

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

Impacted Files	Coverage Δ
...plugin-internal/src/rules/prefer-ast-types-enum.ts
packages/type-utils/src/typeFlagUtils.ts
...ges/typescript-estree/src/create-program/shared.ts
packages/type-utils/src/getTokenAtPosition.ts
...-estree/src/create-program/createProjectProgram.ts
packages/typescript-estree/src/convert.ts
...ript-estree/src/create-program/createSourceFile.ts
packages/type-utils/src/isUnsafeAssignment.ts
...-estree/src/create-program/createDefaultProgram.ts
packages/typescript-estree/src/ts-estree/index.ts
... and 26 more

[JoshuaKGoldberg]

😄 nice find, thanks!