Fix grad higher order handling TupleVariable (#106425)
Previously, we assume the argnums is a **ConstantVariable**. However I accidentally triggered an error on CI where argnums could be a **TupleVariable**. In that case, we have an attribute error when access the .value of argnums.
This PR adds support for the TupleVariable. It allows the unit test to pass without falling back to eager
"PYTORCH_TEST_WITH_DYNAMO=1 python test/functorch/test_eager_transforms.py -k test_argnums_cpu"
Test Plan:
see modified test.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/106425
Approved by: https://github.com/yanboliang, https://github.com/anijain2305, https://github.com/kshitij12345
