Build: changelog update for 8.21.0

CHANGELOG.md

@@ -1,3 +1,15 @@
+v8.21.0 - August 1, 2022
+
+* [`7b43ea1`](https://github.com/eslint/eslint/commit/7b43ea14a8af5fc3dbac38fa9d5bc71741328c16) feat: Implement FlatESLint (#16149) (Nicholas C. Zakas)
+* [`8892511`](https://github.com/eslint/eslint/commit/889251194867b1f394c571a5982249329fa44cfd) chore: Upgrade to Espree 9.3.3 (#16173) (Brandon Mills)
+* [`92bf49a`](https://github.com/eslint/eslint/commit/92bf49a4b39dde728fbc6d348e62c7009e21cf7d) feat: improve the key width calculation in `key-spacing` rule (#16154) (Nitin Kumar)
+* [`c461542`](https://github.com/eslint/eslint/commit/c4615421cb4825e2ad22e275ec9439756d56299c) feat: add new `allowLineSeparatedGroups` option to the `sort-keys` rule (#16138) (Nitin Kumar)
+* [`1cdcbca`](https://github.com/eslint/eslint/commit/1cdcbca8a961a057a9db40df412f249545befe2b) feat: add deprecation warnings for legacy API in `RuleTester` (#16063) (Nitin Kumar)
+* [`0396775`](https://github.com/eslint/eslint/commit/03967755270ae28eec651281c50b6990d3983f48) fix: lines-around-comment apply `allowBlockStart` for switch statements (#16153) (Nitin Kumar)
+* [`2aadc93`](https://github.com/eslint/eslint/commit/2aadc93272f1ab7f40246c6b18c4056660f2b3a2) docs: add anchors to headings inside docs content (#16134) (Strek)
+* [`1233bee`](https://github.com/eslint/eslint/commit/1233beea3938fc4234c8f75917776832226fc3c8) chore: switch to eslint-plugin-node's maintained fork (#16150) (唯然)
+* [`97b95c0`](https://github.com/eslint/eslint/commit/97b95c068d5b35fae68ca919257b61430271ac76) chore: upgrade puppeteer v13 (#16151) (唯然)
+
 v8.20.0 - July 16, 2022
 
 * [`bbf8df4`](https://github.com/eslint/eslint/commit/bbf8df41c901d41753ca4f3f0baf021944782597) chore: Mark autogenerated release blog post as draft (#16130) (Nicholas C. Zakas)