Build(deps): Bump deepmerge in /app/assets/javascripts (#20082)

Bumps [deepmerge](https://github.com/TehShrike/deepmerge) from 4.2.2 to 4.3.0.
- [Release notes](https://github.com/TehShrike/deepmerge/releases)
- [Changelog](https://github.com/TehShrike/deepmerge/blob/master/changelog.md)
- [Commits](https://github.com/TehShrike/deepmerge/compare/v4.2.2...v4.3.0)

---
updated-dependencies:
- dependency-name: deepmerge
  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/package.json

@@ -42,7 +42,7 @@
     "bootstrap": "3.4.1",
     "bootstrap-json": "1.0.0",
     "broccoli-asset-rev": "^3.0.0",
-    "deepmerge": "^4.2.2",
+    "deepmerge": "^4.3.0",
     "dialog-holder": "1.0.0",
     "discourse-common": "1.0.0",
     "discourse-ensure-deprecation-order": "1.0.0",

app/assets/javascripts/yarn.lock

@@ -3516,10 +3516,10 @@ deep-is@^0.1.3, deep-is@~0.1.3:
   resolved "https://registry.yarnpkg.com/deep-is/-/deep-is-0.1.3.tgz#b369d6fb5dbc13eecf524f91b070feedc357cf34"
   integrity sha1-s2nW+128E+7PUk+RsHD+7cNXzzQ=
 
-deepmerge@^4.2.2:
-  version "4.2.2"
-  resolved "https://registry.yarnpkg.com/deepmerge/-/deepmerge-4.2.2.tgz#44d2ea3679b8f4d4ffba33f03d865fc1e7bf4955"
-  integrity sha512-FJ3UgI4gIl+PHZm53knsuSFpE+nESMr7M4v9QcgB7S63Kj/6WqMiFQJpBBYz1Pt+66bZpP3Q7Lye0Oo9MPKEdg==
+deepmerge@^4.3.0:
+  version "4.3.0"
+  resolved "https://registry.yarnpkg.com/deepmerge/-/deepmerge-4.3.0.tgz#65491893ec47756d44719ae520e0e2609233b59b"
+  integrity sha512-z2wJZXrmeHdvYJp/Ux55wIjqo81G5Bp4c+oELTW+7ar6SogWHajt5a9gO3s3IDaGSAXjDk0vlQKN3rms8ab3og==
 
 defaults@^1.0.3:
   version "1.0.3"