migration-test: Use g_free() instead of free()

Signed-off-by: Juan Quintela <quintela@redhat.com>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>

tests/qtest/migration-test.c

@@ -1291,7 +1291,7 @@ static void test_multifd_tcp(void)
     wait_for_serial("dest_serial");
     wait_for_migration_complete(from);
     test_migrate_end(from, to, true);
-    free(uri);
+    g_free(uri);
 }
 
 int main(int argc, char **argv)