fix: update qgpt2_class.py to fix typo

This commit fixes a bug in use_cases_examples/llm/qgpt2_class.py
demo where `simulate` was not called properly.

It raised `TypeError: unsupported operand type(s) for /: 'method' and 'int'`
because `<bound method Circuit.simulate>` was not called.

use_case_examples/llm/qgpt2_class.py

@@ -129,7 +129,7 @@ def run_torch(self, inputs: torch.Tensor, fhe: str = "disable", true_float: bool
                 q_x = np.expand_dims(q_x, axis=0)
 
                 if fhe == "simulate":
-                    q_y = self.circuit.simulate
+                    q_y = self.circuit.simulate(q_x)
 
                 elif fhe == "execute":
                     q_y = self.circuit.encrypt_run_decrypt(q_x)