tart exec: make sure <name> goes after flags like -i and -t in --help (#1090)

Sources/tart/Commands/Exec.swift

@@ -15,15 +15,15 @@ struct Exec: AsyncParsableCommand {
   Note that all non-vanilla Cirrus Labs VM images already have the Tart Guest Agent installed.
   """)
 
-  @Argument(help: "VM name", completion: .custom(completeLocalMachines))
-  var name: String
-
   @Flag(name: [.customShort("i")], help: "Attach host's standard input to a remote command")
   var interactive: Bool = false
 
   @Flag(name: [.customShort("t")], help: "Allocate a remote pseudo-terminal (PTY)")
   var tty: Bool = false
 
+  @Argument(help: "VM name", completion: .custom(completeLocalMachines))
+  var name: String
+
   @Argument(parsing: .captureForPassthrough, help: "Command to execute")
   var command: [String]