Fix a mypy warning

Author: jairov4

mypyc/irbuild/ll_builder.py

@@ -1419,24 +1419,21 @@ def dunder_op(self, lreg: Value, rreg: Value | None, op: str, line: int) -> Valu
         if not isinstance(ltype, RInstance):
             return None
 
-        is_binary = bool(rreg)
-        method_name = op_methods.get(op) if is_binary else unary_op_methods.get(op)
+        method_name = op_methods.get(op) if rreg else unary_op_methods.get(op)
         if method_name is None:
             return None
 
         if not ltype.class_ir.has_method(method_name):
             return None
 
         decl = ltype.class_ir.method_decl(method_name)
-        if not is_binary and len(decl.sig.args) != 1:
+        if not rreg and len(decl.sig.args) != 1:
             return None
 
-        if is_binary and (
-            len(decl.sig.args) != 2 or not is_subtype(rreg.type, decl.sig.args[1].type)
-        ):
+        if rreg and (len(decl.sig.args) != 2 or not is_subtype(rreg.type, decl.sig.args[1].type)):
             return None
 
-        if is_binary and is_subtype(not_implemented_op.type, decl.sig.ret_type):
+        if rreg and is_subtype(not_implemented_op.type, decl.sig.ret_type):
             # If the method is able to return NotImplemented, we should not optimize it.
             # We can just let go so it will be handled through the python api.
             return None