goption: Fix a typo

We presumably want the fallback string used when we cannot determine
the program name to contain balanced angle brackets, as it did before
commit 7098250e.

Fixes: 7098250e "gutils: avoid race setting prgname from g_option_context_parse()/g_application_run()"
Signed-off-by: Simon McVittie <smcv@collabora.com>

glib/goption.c

@@ -1814,7 +1814,7 @@ g_option_context_parse (GOptionContext   *context,
       else
 	prgname = platform_get_argv0 ();
 
-      g_set_prgname_once (prgname ? prgname : "<unknown");
+      g_set_prgname_once (prgname ? prgname : "<unknown>");
 
       g_free (prgname);
     }