Enable NNC fusion for relu6 (#58773)
Summary: Pull Request resolved: https://github.com/pytorch/pytorch/pull/58773
Test Plan:
```
python test/test_ops.py -k relu6
python test/test_jit_fuser_te.py
```
Reviewed By: bertmaher
Differential Revision: D28721791
Pulled By: desertfire
fbshipit-source-id: a94f711977afd080faae052f66eb8dded3cdc79e
