Update dependency eslint to v8.21.0

[renovate[bot]]

This PR contains the following updates:

Package	Change	Age	Adoption	Passing	Confidence
eslint (source)	8.20.0 -> 8.21.0

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Release Notes

eslint/eslint

### [`v8.21.0`](https://togithub.com/eslint/eslint/releases/tag/v8.21.0) [Compare Source](https://togithub.com/eslint/eslint/compare/v8.20.0...v8.21.0) #### Features - [`7b43ea1`](https://togithub.com/eslint/eslint/commit/7b43ea14a8af5fc3dbac38fa9d5bc71741328c16) feat: Implement FlatESLint ([#​16149](https://togithub.com/eslint/eslint/issues/16149)) (Nicholas C. Zakas) - [`92bf49a`](https://togithub.com/eslint/eslint/commit/92bf49a4b39dde728fbc6d348e62c7009e21cf7d) feat: improve the key width calculation in `key-spacing` rule ([#​16154](https://togithub.com/eslint/eslint/issues/16154)) (Nitin Kumar) - [`c461542`](https://togithub.com/eslint/eslint/commit/c4615421cb4825e2ad22e275ec9439756d56299c) feat: add new `allowLineSeparatedGroups` option to the `sort-keys` rule ([#​16138](https://togithub.com/eslint/eslint/issues/16138)) (Nitin Kumar) - [`1cdcbca`](https://togithub.com/eslint/eslint/commit/1cdcbca8a961a057a9db40df412f249545befe2b) feat: add deprecation warnings for legacy API in `RuleTester` ([#​16063](https://togithub.com/eslint/eslint/issues/16063)) (Nitin Kumar) #### Bug Fixes - [`0396775`](https://togithub.com/eslint/eslint/commit/03967755270ae28eec651281c50b6990d3983f48) fix: lines-around-comment apply `allowBlockStart` for switch statements ([#​16153](https://togithub.com/eslint/eslint/issues/16153)) (Nitin Kumar) #### Documentation - [`2aadc93`](https://togithub.com/eslint/eslint/commit/2aadc93272f1ab7f40246c6b18c4056660f2b3a2) docs: add anchors to headings inside docs content ([#​16134](https://togithub.com/eslint/eslint/issues/16134)) (Strek) #### Chores - [`8892511`](https://togithub.com/eslint/eslint/commit/889251194867b1f394c571a5982249329fa44cfd) chore: Upgrade to Espree 9.3.3 ([#​16173](https://togithub.com/eslint/eslint/issues/16173)) (Brandon Mills) - [`1233bee`](https://togithub.com/eslint/eslint/commit/1233beea3938fc4234c8f75917776832226fc3c8) chore: switch to eslint-plugin-node's maintained fork ([#​16150](https://togithub.com/eslint/eslint/issues/16150)) (唯然) - [`97b95c0`](https://togithub.com/eslint/eslint/commit/97b95c068d5b35fae68ca919257b61430271ac76) chore: upgrade puppeteer v13 ([#​16151](https://togithub.com/eslint/eslint/issues/16151)) (唯然)

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