Fixed tests for cpu only platforms (#1259)

* fixed test_4bit_warnings on cpu-only platforms

* fixed linear8bit-based tests for cpu only platforms

tests/test_linear8bitlt.py

@@ -182,7 +182,7 @@ def test_linear_serialization(
 
 
 @pytest.fixture
-def linear8bit():
+def linear8bit(requires_cuda):
     linear = torch.nn.Linear(32, 96)
     linear_custom = Linear8bitLt(
         linear.in_features,

tests/test_modules.py

@@ -616,7 +616,7 @@ def test_fp8linear():
     assert bgraderr < 0.00002
 
 
-def test_4bit_warnings():
+def test_4bit_warnings(requires_cuda):
     dim1 = 64
 
     with pytest.warns(UserWarning, match=r"inference or training"):