use CPU for test_schedule_ring (#9843)

* use CPU for test_schedule_ring

* why pre-commit is good

test/unit/test_allreduce.py

@@ -1,5 +1,5 @@
 import unittest
-from tinygrad import Tensor, Device
+from tinygrad import Tensor
 from tinygrad.helpers import Context
 from tinygrad.ops import Ops
 
@@ -7,7 +7,7 @@ class TestRingAllReduce(unittest.TestCase):
   def test_schedule_ring(self):
     with Context(RING=2):
       N = 6
-      ds = tuple(f"{Device.DEFAULT}:{i}" for i in range(N))
+      ds = tuple(f"CPU:{i}" for i in range(N))
       t = Tensor.empty(N, N*100).shard(ds, axis=0).realize()
       schedules = t.sum(0).schedule_with_vars()[0]
       copies = [si for si in schedules if si.ast.op is Ops.COPY]