Part of: https://github.com/eslint/rfcs/tree/main/designs/2021-stricter-rule-test-validation#disallow-identical-test-cases

* main:
  chore: Split Docs CI from core CI (eslint#17897)
  fix: Ensure config keys are printed for config errors (eslint#17980)
  chore: delete relative-module-resolver.js (eslint#17981)
  docs: migration guide entry for `no-inner-declarations` (eslint#17977)
  docs: Update README
  feat: maintain latest ecma version in ESLint (eslint#17958)
  feat!: no-inner-declaration new default behaviour and option (eslint#17885)
  feat: add `no-useless-assignment` rule (eslint#17625)
  fix: `no-misleading-character-class` edge cases with granular errors (eslint#17970)
  feat: `no-misleading-character-class` granular errors (eslint#17515)
  docs: fix number of code-path events on custom rules page (eslint#17969)
  docs: reorder entries in v9 migration guide (eslint#17967)
  fix!: handle `--output-file` for empty output when saving to disk (eslint#17957)

* main:
  docs: Update note about ECMAScript support (eslint#17991)
  chore: update `markdownlint` to `v0.33.0` (eslint#17995)
  docs: Update release blog post template (eslint#17994)
  docs: Add sections on non-npm plugin configuration (eslint#17984)
  9.0.0-alpha.1
  Build: changelog update for 9.0.0-alpha.1
  chore: package.json update for @eslint/js release