[5.1.x] Corrected wording in docs/ref/models/constraints.txt.

Backport of 579a1c9 from main.

Author: violuke

docs/ref/models/constraints.txt

@@ -210,7 +210,7 @@ enforced immediately after every command.
 .. admonition:: MySQL, MariaDB, and SQLite.
 
     Deferrable unique constraints are ignored on MySQL, MariaDB, and SQLite as
-    neither supports them.
+    they do not support them.
 
 .. warning::