Added literal tag for RETURNING

This is an old mistake (92e38182d7); backpatch all the way back.

Author: Atsushi Torikoshi <torikoshia@oss.nttdata.com>
Reviewed-by: Ashutosh Bapat <ashutosh.bapat.oss@gmail.com>
Discussion: https://postgr.es/m/c0aa00b60a16c0ea2a4c5123b013acb9@oss.nttdata.com

doc/src/sgml/ref/copy.sgml

@@ -128,10 +128,10 @@ COPY { <replaceable class="parameter">table_name</replaceable> [ ( <replaceable
      </para>
      <para>
       For <command>INSERT</command>, <command>UPDATE</command> and
-      <command>DELETE</command> queries a RETURNING clause must be provided,
-      and the target relation must not have a conditional rule, nor
-      an <literal>ALSO</literal> rule, nor an <literal>INSTEAD</literal> rule
-      that expands to multiple statements.
+      <command>DELETE</command> queries a <literal>RETURNING</literal> clause
+      must be provided, and the target relation must not have a conditional
+      rule, nor an <literal>ALSO</literal> rule, nor an
+      <literal>INSTEAD</literal> rule that expands to multiple statements.
      </para>
     </listitem>
    </varlistentry>