foot: set PATH in server's systemd unit file

If not set, foot's terminal spawning shortcut will not work as the
`footclient` binary is not on the server's PATH.

modules/programs/foot.nix

@@ -68,6 +68,7 @@ in {
         };
 
         Service = {
+          Environment = "PATH=${makeBinPath [ cfg.package ]}";
           ExecStart = "${cfg.package}/bin/foot --server";
           Restart = "on-failure";
           OOMPolicy = "continue";

tests/modules/programs/foot/systemd-user-service-expected.service

@@ -2,6 +2,7 @@
 WantedBy=graphical-session.target
 
 [Service]
+Environment=PATH=@foot@/bin
 ExecStart=@foot@/bin/foot --server
 OOMPolicy=continue
 Restart=on-failure