🐛 Fixed theme uploads freezing when folders are read-only (#28898)

ref https://linear.app/ghost/issue/ONC-1838
ref TryGhost/framework#761
ref TryGhost/gscan#853

Theme uploads could hang without any visible error when a zip contained
folders without sufficient write permissions. GScan needs to write into
those folders while extracting and validating the theme.

Updated `gscan` to include the permission handling fix so missing
permissions are restored during upload and the theme can be installed
successfully instead of leaving the UI frozen.

Author: sagzy

ghost/core/package.json

@@ -176,7 +176,7 @@
     "ghost-storage-base": "2.1.0",
     "glob": "catalog:",
     "got": "13.0.0",
-    "gscan": "6.4.0",
+    "gscan": "6.4.1",
     "handlebars": "4.7.9",
     "heic-convert": "2.1.0",
     "html-to-text": "5.1.1",