Unary operators show `unary` twice on diff

[FMorschel]

Describe the bug
Unary operators show up as unaryunary- (or whatever operator) instead of simply unary-.

To Reproduce

class MyClass {}

class MyClass {
  @override
  int operator -() => 0;
}

Actual and Expected behavior
It should show unary only once.

System info (please complete the following information):

• Dart SDK version: 3.9.0-edge.d3c323e26d1663ab422ff89b65d5a78b0e89c997 (main) (Sun Jul 6 22:55:04 2025 -0700) on "windows_x64"
• dart_apitool version 0.21.1