e2e: use valid jobspec for group check test (#6967)

Group service checks cannot interpolate task fields, because the task
fields are not available at the time the script check hook is created
for the group service. When f31482a was merged this e2e test began
failing because we are now correctly matching the script check ID to
the service ID, which revealed this jobspec was invalid.

e2e/consul/input/checks_group.nomad

@@ -51,7 +51,7 @@ job "group_check" {
         interval = "2s"
         timeout  = "2s"
         command  = "cat"
-        args     = ["${NOMAD_TASK_DIR}/alive-2b"]
+        args     = ["alive-2b"]
       }
     }