Fixed #29414 -- Restored form inputs on admin inlines when the user doesn't have the change permission.

Regression in 825f0beda8.

tests/admin_inlines/models.py

@@ -159,6 +159,12 @@ class Novel(models.Model):
     name = models.CharField(max_length=40)
 
 
+class NovelReadonlyChapter(Novel):
+
+    class Meta:
+        proxy = True
+
+
 class Chapter(models.Model):
     name = models.CharField(max_length=40)
     novel = models.ForeignKey(Novel, models.CASCADE)