Need to relax tolerance for a few float64 nvfuser grad tests

Nobody has claimed this yet.

```
=========================== short test summary info ============================
FAILED thunder/tests/test_grad.py::test_vjp_correctness_softsign_nvfuser_cuda_thunder.dtypes.float64 - AssertionError: Scalars are not close!

Expected 0.0015554002273835033 but got 0.001591950186688797.
Absolute difference: 3.654995930529371e-05 (up to 1e-07 allowed)
Relative difference: 0.023498748850498824 (up to 1e-07 allowed)
FAILED thunder/tests/test_grad.py::test_vjp_correctness_normalize_nvfuser_cuda_thunder.dtypes.float64 - AssertionError: Scalars are not close!

Expected 2.9702087605694922 but got 2.970201815694213.
Absolute difference: 6.9448752793022095e-06 (up to 1e-07 allowed)
Relative difference: 2.338177494961881e-06 (up to 1e-07 allowed)
FAILED thunder/tests/test_grad.py::test_vjp_correctness_abs_nvfuser_cuda_thunder.dtypes.float64 - AssertionError: Scalars are not close!

Expected 0.09839208072782858 but got 0.09824138678418542.
Absolute difference: 0.00015069394364315702 (up to 1e-07 allowed)
Relative difference: 0.0015315657777377983 (up to 1e-07 allowed)
= 3 failed, 733 passed, 55 skipped, 23 xfailed, 15 xpassed, 92422 warnings in 839.96s (0:13:59) =
```

CI - https://dev.azure.com/Lightning-AI/lightning/_build/results?buildId=238959&view=logs&j=83d7ca60-c2d2-50c8-1ed9-9f99750fc4f0&t=d88aa08c-a7b7-5504-bdb7-50942829cc54

cc @tfogal @mruberry

Start with the three failing cases in thunder/tests/test_grad.py: test_vjp_correctness_softsign_nvfuser_cuda_thunder, test_vjp_correctness_normalize_nvfuser_cuda_thunder, and test_vjp_correctness_abs_nvfuser_cuda_thunder, using the linked CI failure as context. Adjust their float64 tolerance as needed and rerun these tests; done means the three failures pass without causing regressions in the surrounding test file.

Written by the indexing model from the issue text.