fork-journal: use char* const* for strv input param

This is compatible with char** and is what I originally
asked for in
https://github.com/systemd/systemd/pull/36858#discussion_r2086792739
Someone needs to read better ;-)

src/systemctl/systemctl-start-unit.c

@@ -394,7 +394,7 @@ int verb_start(int argc, char *argv[], void *userdata) {
                 ret = enqueue_marked_jobs(bus, w);
         else {
                 if (arg_verbose)
-                        (void) journal_fork(arg_runtime_scope, (const char**) names, &journal_pid);
+                        (void) journal_fork(arg_runtime_scope, names, &journal_pid);
 
                 STRV_FOREACH(name, names) {
                         _cleanup_(sd_bus_error_free) sd_bus_error error = SD_BUS_ERROR_NULL;