Update from shakapacker v6.0.0.rc13 to v6.5.0

Using a two-step process is recommended:
332e25186a/docs/v6_upgrade.md

package.json

@@ -31,7 +31,7 @@
     "rails-erb-loader": "^5.5.2",
     "sass": "^1.54.4",
     "sass-loader": "^13.0.2",
-    "shakapacker": "^6.0.0-rc.14",
+    "shakapacker": "6.5.0",
     "sortablejs": "^1.15.0",
     "style-loader": "^3.3.1",
     "terser-webpack-plugin": "5",
@@ -40,7 +40,8 @@
     "webpack": "5",
     "webpack-assets-manifest": "5",
     "webpack-cli": "4",
-    "webpack-merge": "5"
+    "webpack-merge": "5",
+    "webpack-sources": "^3.2.3"
   },
   "devDependencies": {
     "webpack-dev-server": "^4.10.0"