Temporarily skip sys.geom.class.multipath.failloop.failloop in CI

This test case uses `dtrace -c` but it has some issues at the moment so
disable it until dtrace fixed.

From markj:

This is the CTF type ID limit which has come up quite a few times
lately.  It'll be fixed with the introduction of CTFv3.

PR:		258763
Sponsored by:	The FreeBSD Foundation

tests/sys/geom/class/multipath/failloop.sh

@@ -36,6 +36,10 @@ failloop_head()
 }
 failloop_body()
 {
+	if [ "$(atf_config_get ci false)" = "true" ]; then
+		atf_skip "https://bugs.freebsd.org/258763"
+	fi
+
 	sysctl -n kern.geom.notaste > kern.geom.notaste.txt
 	load_gnop
 	load_gmultipath