selftests: net: add msg_oob to gitignore

This executable is missing from the corresponding gitignore file.
Add msg_oob to the net gitignore list.

Signed-off-by: Javier Carrasco <javier.carrasco.cruz@gmail.com>
Link: https://patch.msgid.link/20241005-net-selftests-gitignore-v2-1-3a0b2876394a@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

tools/testing/selftests/net/.gitignore

@@ -16,6 +16,7 @@ ipsec
 ipv6_flowlabel
 ipv6_flowlabel_mgr
 log.txt
+msg_oob
 msg_zerocopy
 ncdevmem
 nettest