fix: add availability permissions for can_view_group (#3850)

Author: falbru

lego/apps/lending/permissions.py

@@ -5,6 +5,8 @@
 class LendableObjectPermissionHandler(PermissionHandler):
     default_keyword_permission = "/sudo/admin/lendableobjects/{perm}/"
 
+    safe_methods = [VIEW, LIST, "availability"]
+
 
 class LendingRequestPermissionHandler(PermissionHandler):
     default_keyword_permission = "/sudo/admin/lendingrequests/{perm}/"