Fix TypeError in MutableTorchTensorRTModule on Python 3.9

[HolyWu]

Description

    import torch_tensorrt as torchtrt
/__w/_temp/conda_environment_10423996349/lib/python3.9/site-packages/torch_tensorrt/__init__.py:137: in <module>
    from torch_tensorrt.dynamo.runtime._MutableTorchTensorRTModule import (
/__w/_temp/conda_environment_10423996349/lib/python3.9/site-packages/torch_tensorrt/dynamo/runtime/_MutableTorchTensorRTModule.py:40: in <module>
    class MutableTorchTensorRTModule(object):
/__w/_temp/conda_environment_10423996349/lib/python3.9/site-packages/torch_tensorrt/dynamo/runtime/_MutableTorchTensorRTModule.py:61: in MutableTorchTensorRTModule
    Set[torch.dtype | dtype] | Tuple[torch.dtype | dtype]
E   TypeError: unsupported operand type(s) for |: 'type' and 'EnumMeta'

Type union operator was not supported on Python 3.9 since it's introduced on Python 3.10. Additionally, the allowed type for enabled_precisions should only be Set, not Tuple.

Type of change

• Bug fix (non-breaking change which fixes an issue)

Checklist:

• My code follows the style guidelines of this project (You can use the linters)
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas and hacks
• I have made corresponding changes to the documentation
• I have added tests to verify my fix or my feature
• New and existing unit tests pass locally with my changes
• I have added the relevant labels to my PR in so that relevant reviewers are notified

[narendasan]

LGTM, Thanks!