ci: no fetch in backend tests (#16438)

should make for less actions cache thrashing

extra/torch_backend/test.py

@@ -240,9 +240,9 @@ class TestTorchBackend(unittest.TestCase):
     np.testing.assert_equal(result.cpu().numpy(), [3., 3., 2.])
 
   def test_mnist_index(self):
+    # from tinygrad.nn.datasets import mnist
+    X_train, Y_train = Tensor.randint(60000, 1, 28, 28, dtype='uchar').realize(), Tensor.randint(60000, dtype='uchar').realize()
     GlobalCounters.reset()
-    from tinygrad.nn.datasets import mnist
-    X_train, Y_train, _, _ = mnist()
     X_train = torch.tensor(X_train.float().numpy(), device=device)
     Y_train = torch.tensor(Y_train.cast('int64').numpy(), device=device)
     samples = torch.randint(0, X_train.shape[0], (32,))

test/backend/test_arange.py

@@ -125,8 +125,8 @@ class TestIndexing(unittest.TestCase):
   def test_index_mnist(self, noopt=1, op_limit=512*784*13, split_reduceop=0):
     # WEBGPU generates more ops due to bitpacking of < 4-byte dtypes
     if Device.DEFAULT == "WEBGPU": op_limit *= 15
-    from tinygrad.nn.datasets import mnist
-    X_train, Y_train, _, _ = mnist()
+    # from tinygrad.nn.datasets import mnist
+    X_train, Y_train = Tensor.randint(DSET, 1, 28, 28, dtype='uchar').realize(), Tensor.randint(DSET, dtype='uchar').realize()
     with Context(NOOPT=noopt, SPLIT_REDUCEOP=split_reduceop):
       samples = Tensor.randint(getenv("BS", 512), high=X_train.shape[0]).realize()
       GlobalCounters.reset()

test/backend/test_schedule.py

@@ -1059,9 +1059,9 @@ class TestSchedule(unittest.TestCase):
     self.assertEqual(b.tolist(), [False, False])
 
   def test_mnist_val(self):
-    from tinygrad.nn.datasets import mnist
+    # from tinygrad.nn.datasets import mnist
     import torch
-    _, Y_train, _, _ = mnist()
+    Y_train = Tensor.randint(60000, dtype='uchar').realize()
     samples = Tensor.randint(BS:=getenv("BS", 512), high=cast(int,Y_train.shape[-1])).realize()
     yt = Tensor.randn(BS, 10).realize()
     loss = yt.sparse_categorical_crossentropy(Y_train[samples])