Bump doorkeeper from 5.6.3 to 5.6.4 (#23422)

Bumps [doorkeeper](https://github.com/doorkeeper-gem/doorkeeper) from 5.6.3 to 5.6.4.
- [Release notes](https://github.com/doorkeeper-gem/doorkeeper/releases)
- [Changelog](https://github.com/doorkeeper-gem/doorkeeper/blob/main/CHANGELOG.md)
- [Commits](https://github.com/doorkeeper-gem/doorkeeper/compare/v5.6.3...v5.6.4)

---
updated-dependencies:
- dependency-name: doorkeeper
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

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Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Gemfile.lock

@@ -207,7 +207,7 @@ GEM
     docile (1.4.0)
     domain_name (0.5.20190701)
       unf (>= 0.0.5, < 1.0.0)
-    doorkeeper (5.6.3)
+    doorkeeper (5.6.4)
       railties (>= 5)
     dotenv (2.8.1)
     dotenv-rails (2.8.1)