feat: allow webpack-merge v6 (#502)

Author: G-Rath

CHANGELOG.md

@@ -12,6 +12,7 @@ Changes since the last non-beta release.
 
 ### Changed
 - Update outdated GitHub Actions to use Node.js 20.0 versions instead [PR 497](https://github.com/shakacode/shakapacker/pull/497) by [adriangohjw](https://github.com/adriangohjw).
+- Allow `webpack-merge` v6 to be used [PR 502](https://github.com/shakacode/shakapacker/pull/502) by [G-Rath](https://github.com/g-rath).
 
 ### Fixed
 

package.json

@@ -62,7 +62,7 @@
     "webpack-assets-manifest": "^5.0.6",
     "webpack-cli": "^4.9.2 || ^5.0.0",
     "webpack-dev-server": "^4.9.0 || ^5.0.0",
-    "webpack-merge": "^5.8.0"
+    "webpack-merge": "^5.8.0 || ^6.0.0"
   },
   "peerDependenciesMeta": {
     "@types/babel__core": {