Bump webpack-merge from 4.2.2 to 5.8.0

Bumps [webpack-merge](https://github.com/survivejs/webpack-merge) from 4.2.2 to 5.8.0.
- [Release notes](https://github.com/survivejs/webpack-merge/releases)
- [Changelog](https://github.com/survivejs/webpack-merge/blob/develop/CHANGELOG.md)
- [Commits](survivejs/webpack-merge@v4.2.2...v5.8.0)

---
updated-dependencies:
- dependency-name: webpack-merge
  dependency-type: direct:development
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <support@github.com>

package.json

@@ -49,7 +49,7 @@
     "web-ext-types": "^3.2.1",
     "webpack": "5.0.0",
     "webpack-cli": "^4.10.0",
-    "webpack-merge": "^4.1.3"
+    "webpack-merge": "^5.8.0"
   },
   "dependencies": {
     "@material-ui/icons": "4.0.1",

yarn.lock

@@ -6880,14 +6880,7 @@ webpack-log@^2.0.0:
     ansi-colors "^3.0.0"
     uuid "^3.3.2"
 
-webpack-merge@^4.1.3:
-  version "4.2.2"
-  resolved "https://registry.yarnpkg.com/webpack-merge/-/webpack-merge-4.2.2.tgz#a27c52ea783d1398afd2087f547d7b9d2f43634d"
-  integrity sha512-TUE1UGoTX2Cd42j3krGYqObZbOD+xF7u28WB7tfUordytSjbWTIjK/8V0amkBfTYN4/pB/GIDlJZZ657BGG19g==
-  dependencies:
-    lodash "^4.17.15"
-
-webpack-merge@^5.7.3:
+webpack-merge@^5.7.3, webpack-merge@^5.8.0:
   version "5.8.0"
   resolved "https://registry.yarnpkg.com/webpack-merge/-/webpack-merge-5.8.0.tgz#2b39dbf22af87776ad744c390223731d30a68f61"
   integrity sha512-/SaI7xY0831XwP6kzuwhKWVKDP9t1QY1h65lAFLbZqMPIuYcD9QAW4u9STIbU9kaJbPBB/geU/gLr1wDjOhQ+Q==