Fixed #34842 -- Fixed ModelAdmin.readonly_fields crash with GeneratedFields.

tests/admin_views/admin.py

@@ -119,6 +119,7 @@ from .models import (
     Simple,
     Sketch,
     Song,
+    Square,
     State,
     Story,
     StumpJoke,
@@ -1175,6 +1176,10 @@ class TravelerAdmin(admin.ModelAdmin):
     autocomplete_fields = ["living_country"]
 
 
+class SquareAdmin(admin.ModelAdmin):
+    readonly_fields = ("area",)
+
+
 site = admin.AdminSite(name="admin")
 site.site_url = "/my-site-url/"
 site.register(Article, ArticleAdmin)
@@ -1298,6 +1303,7 @@ site.register(UserProxy)
 site.register(Box)
 site.register(Country, CountryAdmin)
 site.register(Traveler, TravelerAdmin)
+site.register(Square, SquareAdmin)
 
 # Register core models we need in our tests
 site.register(User, UserAdmin)