add vsock-mux/* in ssh config drop-in

systemd#32941
added support for firecracker/cloud-hypervisor and
their unix-domain socket to AF_VSOCK multiplex.

but I forgot to add the pattern in the ssh config drop-in.
fix it now!

src/ssh-generator/20-systemd-ssh-proxy.conf.in

@@ -9,7 +9,7 @@ Host .host machine/.host
 # Make sure unix/* and vsock/* can be used to connect to AF_UNIX and AF_VSOCK paths.
 # Make sure machine/* can be used to connect to local machines registered in machined.
 #
-Host unix/* vsock/* machine/*
+Host unix/* vsock/* vsock-mux/* machine/*
         ProxyCommand {{LIBEXECDIR}}/systemd-ssh-proxy %h %p
         ProxyUseFdpass yes
         CheckHostIP no