Cleanup: correct API usage for script access

In practice this didn't cause problems, but accessing scripts via
bpy.utils.resource_path('USER') ignores the BLENDER_USER_SCRIPTS
environment variable.

tests/python/bl_load_addons.py

@@ -14,7 +14,7 @@ import sys
 import importlib
 
 BLACKLIST_DIRS = (
-    os.path.join(bpy.utils.resource_path('USER'), "scripts"),
+    bpy.utils.user_resource('SCRIPTS'),
 ) + tuple(addon_utils.paths()[1:])
 BLACKLIST_ADDONS = set()