Update on "Update phi-3-mini to use the export library"

as title.

Note: exporting model from HF is currently blocked by this issue, https://fburl.com/qpaapajr. We need to apply the following trick to export the model.
```
        model = torch.export._trace._export(
            model,
            example_inputs,
            dynamic_shapes=dynamic_shape,
            strict=False,
            pre_dispatch=False,
        )
```

Differential Revision: [D59503255](https://our.internmc.facebook.com/intern/diff/D59503255/)

[ghstack-poisoned]

Author: helunwencser

examples/models/phi-3-mini/export_phi-3-mini.py

@@ -14,13 +14,13 @@
     PT2EQuantOptions,
 )
 
-# pyre-ignore: Undefined attribute [16]: Module `transformers` has no attribute `Phi3ForCausalLM`
 from transformers import Phi3ForCausalLM
 
 
 def main() -> None:
     torch.manual_seed(42)
 
+    # pyre-ignore: Undefined attribute [16]: Module `transformers` has no attribute `Phi3ForCausalLM`
     model = Phi3ForCausalLM.from_pretrained("microsoft/Phi-3-mini-4k-instruct")
 
     modelname = "phi-3-mini"