doc: Fix typo in pg_amcheck for term "schema"

Author: Alexander Lakhin
Discussion: https://postgr.es/m/e8c38840-596a-83d6-bd8d-cebc51111572@gmail.com
Backpatch-through: 14

Author: michaelpq

doc/src/sgml/ref/pg_amcheck.sgml

@@ -160,7 +160,7 @@ PostgreSQL documentation
        Patterns may be unqualified, e.g. <literal>myrel*</literal>, or they
        may be schema-qualified, e.g. <literal>myschema*.myrel*</literal> or
        database-qualified and schema-qualified, e.g.
-       <literal>mydb*.myscheam*.myrel*</literal>. A database-qualified
+       <literal>mydb*.myschema*.myrel*</literal>. A database-qualified
        pattern will add matching databases to the list of databases to be
        checked.
       </para>