Corrected admin check IDs in docs.

Author: felixxm

docs/ref/checks.txt

@@ -827,11 +827,11 @@ The following checks are performed on any
 :class:`~django.contrib.contenttypes.admin.GenericInlineModelAdmin` that is
 registered as an inline on a :class:`~django.contrib.admin.ModelAdmin`.
 
-* **admin.E301**: ``'ct_field'`` references ``<label>``, which is not a field
+* **admin.E301**: ``<model>`` has no ``GenericForeignKey``.
+* **admin.E302**: ``'ct_field'`` references ``<label>``, which is not a field
   on ``<model>``.
-* **admin.E302**: ``'ct_fk_field'`` references ``<label>``, which is not a
+* **admin.E303**: ``'ct_fk_field'`` references ``<label>``, which is not a
   field on ``<model>``.
-* **admin.E303**: ``<model>`` has no ``GenericForeignKey``.
 * **admin.E304**: ``<model>`` has no ``GenericForeignKey`` using content type
   field ``<field name>`` and object ID field ``<field name>``.