Build(deps): Bump @babel/core in /app/assets/javascripts (#20381)

Bumps [@babel/core](https://github.com/babel/babel/tree/HEAD/packages/babel-core) from 7.20.12 to 7.21.0.
- [Release notes](https://github.com/babel/babel/releases)
- [Changelog](https://github.com/babel/babel/blob/main/CHANGELOG.md)
- [Commits](https://github.com/babel/babel/commits/v7.21.0/packages/babel-core)

---
updated-dependencies:
- dependency-name: "@babel/core"
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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

app/assets/javascripts/discourse-plugins/package.json

@@ -17,7 +17,7 @@
     "webpack": "^5.75.0"
   },
   "devDependencies": {
-    "@babel/core": "^7.20.12"
+    "@babel/core": "^7.21.0"
   },
   "engines": {
     "node": "16.* || >= 18",