Adjust QuantumError.to_dict() to handle lack of Instruction.condition

In Qiskit 2.0 the Instruction.condition attribute will be removed
following it's deprecation in 1.3.0. This attribute has been superseded
by the IfElseOp which covers the use case but offers more functionality.
The removal is pending in Qiskit/qiskit#13506 and the use of qiskit-aer
in Qiskit's tests is blocking progress on that PR. This commit makes the
usage of .condition optional to maintain compatibility with Qiskit<2.0
but also work in >=2.0 with the attribute removed.

qiskit_aer/noise/errors/quantum_error.py

@@ -319,8 +319,9 @@ def to_dict(self):
                     inst_dict["params"] = inst.operation.params
                 if inst.operation.label:
                     inst_dict["label"] = inst.operation.label
-                if inst.operation.condition:
-                    inst_dict["condition"] = inst.operation.condition
+                condition = getattr(inst.operation, "condition", None)
+                if condition:
+                    inst_dict["condition"] = condition
                 circ_inst.append(inst_dict)
             instructions.append(circ_inst)
         # Construct error dict