[pruning] Add gelu to list of supported activation functions (#95618)
Summary:
This PR adds nn.GELU and F.gelu respectively to the list of suppported
activation functions
Test Plan:
```
python test/test_ao_sparsity.py -- TestBaseSparsifier
```
Pull Request resolved: https://github.com/pytorch/pytorch/pull/95618
Approved by: https://github.com/andrewor14
