Add MarlGrid make smoke coverage

Author: tortoise10101

envpool/make_test.py

@@ -69,6 +69,7 @@
     "envpool.gfootball": ("gfootball/academy_empty_goal_close-v1",),
     "envpool.highway": ("HighwayFast-v0",),
     "envpool.jumanji": ("Game2048-v1",),
+    "envpool.marlgrid": ("Goalcycle-demo-solo-v0",),
     "envpool.minigrid": ("MiniGrid-DoorKey-8x8-v0",),
     "envpool.mujoco.dmc": ("WalkerWalk-v1",),
     "envpool.mujoco.gym": ("Ant-v5",),