chore(deps): update eslint monorepo to ^9.21.0

[renovate]

This PR contains the following updates:

Package	Change	Age	Adoption	Passing	Confidence
@eslint/js (source)	^9.20.0 -> ^9.21.0
eslint (source)	^9.20.1 -> ^9.21.0

---

Release Notes

eslint/eslint (@​eslint/js)

v9.21.0

Compare Source

Features

• 418717f feat: introduce new deprecated types for rules (#​19238) (fnx)
• 5c5b802 feat: Add --ext CLI option (#​19405) (Milos Djermanovic)

Bug Fixes

• db5340d fix: update missing plugin message template (#​19445) (Milos Djermanovic)
• d8ffdd4 fix: do not exit process on rule crash (#​19436) (Francesco Trotta)

Documentation

• c5561ea docs: Update README (GitHub Actions Bot)
• 80b0485 docs: replace var with let and const in rule example (#​19434) (Tanuj Kanti)
• f67d5e8 docs: Update README (GitHub Actions Bot)
• 75afc61 docs: Update README (GitHub Actions Bot)
• 0636cab docs: Update Eleventy from v2 to v3 (#​19415) (Amaresh S M)
• dd7d930 docs: Update README (GitHub Actions Bot)

Chores

• a8c9a9f chore: update @eslint/eslintrc and @eslint/js (#​19453) (Francesco Trotta)
• 265e0cf chore: package.json update for @​eslint/js release (Jenkins)
• 3401b85 test: add test for Rule.ReportDescriptor type (#​19449) (Francesco Trotta)
• e497aa7 chore: update rewrite dependencies (#​19448) (Francesco Trotta)
• dab5478 chore: better error message for missing plugin in config (#​19402) (Tanuj Kanti)
• ebfe2eb chore: set js language for bug report issue config block (#​19439) (Josh Goldberg ✨)
• 5fd211d test: processors can return subpaths (#​19425) (Milos Djermanovic)

---

Configuration

📅 Schedule: Branch creation - "on thursday" in timezone Asia/Kolkata, Automerge - At any time (no schedule defined).

🚦 Automerge: Enabled.

♻ Rebasing: Whenever PR is behind base branch, or you tick the rebase/retry checkbox.

🔕 Ignore: Close this PR and you won't be reminded about these updates again.

---

• If you want to rebase/retry this PR, check this box

---

This PR was generated by Mend Renovate. View the repository job log.