[2.1.x] Fixed #29487 -- Accounted for object level permissions when calculating change view's read-only fields.

Thanks Matthew Frazier for the report and fix.

Backport of 553617e613 from master

tests/admin_views/admin.py

@@ -1116,3 +1116,13 @@ site6.register(Article, ArticleAdmin6)
 site6.register(Actor, ActorAdmin6)
 site6.register(Chapter, ChapterAdmin6)
 site6.register(Color, ColorAdmin6)
+
+
+class ArticleAdmin9(admin.ModelAdmin):
+    def has_change_permission(self, request, obj=None):
+        # Simulate that the user can't change a specific object.
+        return obj is None
+
+
+site9 = admin.AdminSite(name='admin9')
+site9.register(Article, ArticleAdmin9)