Fix #106840: Add-ons not loading from custom script directories

`script_paths()` wasn't updated correctly, but that was hidden by some
compabtibility logic that was in the patch earlier. Only with my last
change to the PR before merging it that was removed and the error became
quite visible.

scripts/modules/bpy/utils/__init__.py

@@ -355,7 +355,7 @@ def script_paths(*, subdir=None, user_pref=True, check_all=False, use_user=True)
 
     :arg subdir: Optional subdir.
     :type subdir: string
-    :arg user_pref: Include the user preference script path.
+    :arg user_pref: Include the user preference script paths.
     :type user_pref: bool
     :arg check_all: Include local, user and system paths rather just the paths Blender uses.
     :type check_all: bool
@@ -387,6 +387,9 @@ def script_paths(*, subdir=None, user_pref=True, check_all=False, use_user=True)
         if use_user:
             base_paths.append(path_user)
 
+    if user_pref:
+        base_paths.extend(script_paths_pref())
+
     scripts = []
     for path in base_paths:
         if not path: