[CI] Install dill in ci (#116214)

Pull Request resolved: https://github.com/pytorch/pytorch/pull/116214
Approved by: https://github.com/malfet
ghstack dependencies: #116230

torch/testing/_internal/common_utils.py

@@ -96,6 +96,7 @@ from torch.testing._comparison import (
 )
 from torch.testing._comparison import not_close_error_metas
 from torch.testing._internal.common_dtype import get_all_dtypes
+from torch.utils._import_utils import _check_module_exists
 import torch.utils._pytree as pytree
 
 from .composite_compliance import no_dispatch
@@ -1224,20 +1225,6 @@ else:
 
 IS_FILESYSTEM_UTF8_ENCODING = sys.getfilesystemencoding() == 'utf-8'
 
-def _check_module_exists(name: str) -> bool:
-    r"""Returns if a top-level module with :attr:`name` exists *without**
-    importing it. This is generally safer than try-catch block around a
-    `import X`. It avoids third party libraries breaking assumptions of some of
-    our tests, e.g., setting multiprocessing start method when imported
-    (see librosa/#747, torchvision/#544).
-    """
-    try:
-        import importlib.util
-        spec = importlib.util.find_spec(name)
-        return spec is not None
-    except ImportError:
-        return False
-
 TEST_NUMPY = _check_module_exists('numpy')
 TEST_FAIRSEQ = _check_module_exists('fairseq')
 TEST_SCIPY = _check_module_exists('scipy')
@@ -1265,6 +1252,9 @@ def split_if_not_empty(x: str):
 
 NOTEST_CPU = "cpu" in split_if_not_empty(os.getenv('PYTORCH_TESTING_DEVICE_EXCEPT_FOR', ''))
 
+skipIfNoDill = unittest.skipIf(not TEST_DILL, "no dill")
+
+
 # Python 2.7 doesn't have spawn
 TestEnvironment.def_flag("NO_MULTIPROCESSING_SPAWN", env_var="NO_MULTIPROCESSING_SPAWN")
 TestEnvironment.def_flag("TEST_WITH_ASAN", env_var="PYTORCH_TEST_WITH_ASAN")