Fix the variable name in postgresql_pkg_tests.sh

Originally reported in https://bugzilla.redhat.com/show_bug.cgi?id=1803696

Author: hhorak

share/postgresql-setup/postgresql_pkg_tests.sh.in

@@ -152,7 +152,7 @@ pgtests_start ()
             fi
         done
 
-        createdb "$_db" --owner "$_part"
+        createdb "$_db" --owner "$_user"
 
         IFS=$save_IFS
     done