Fix buildfarm failure introduced by commit e65dbc9.

The patch had incorrectly specified the default value for
publish_generated_columns during the query formation in pg_dump.

Author: Vignesh C <vignesh21@gmail.com>
Discussion: https://postgr.es/m/CAA4eK1KfZYTD8Hpi9TD1KaB8rNUBR9baUvTxa5wYyZDGbEaa6g@mail.gmail.com

Author: Amit Kapila

src/bin/pg_dump/pg_dump.c

@@ -4318,7 +4318,7 @@ getPublications(Archive *fout)
 	if (fout->remoteVersion >= 180000)
 		appendPQExpBufferStr(query, "p.pubgencols_type ");
 	else
-		appendPQExpBufferStr(query, CppAsString2(PUBLISH_GENCOLS_NONE) " AS pubgencols_type ");
+		appendPQExpBuffer(query, "'%c' AS pubgencols_type ", PUBLISH_GENCOLS_NONE);
 
 	appendPQExpBufferStr(query, "FROM pg_publication p");