isNot matcher is not negating the result of a wraped matcher #1637

pubspec.yaml as

dev_dependencies:
  flutter_test:
    sdk: flutter

main(){
  test("given a async closure that dosnt throw, then it shouldnt throw", () async {
    await expectLater(() => Future.value("this dosnt throw and just returns"), isNot(throwsA(anything)));
  });

  test("samezys just with expect", () {
    expect(() => Future.value("same"), isNot(throwsA(anything)));
  });

  test("given sync funcs, the test should detect throwing", () {
    expect(() => "test", isNot(throwsA(anything)));
    expect(() => throw Error(), throwsA(anything));
  });

  test("given a throwing future, then the closure should throw", (){
    expect(() => Future.error(Error()), throwsA(anything));
  });
}

[√] Android toolchain - develop for Android devices (Android SDK version 31.0.0)
• Android SDK at C:\Users\user\AppData\Local\Android\Sdk
• Platform android-31, build-tools 31.0.0
• ANDROID_SDK_ROOT = C:\Users\user\AppData\Local\Android\Sdk
• Java binary at: C:\Program Files\Android\Android Studio\jre\bin\java
• Java version OpenJDK Runtime Environment (build 11.0.10+0-b96-7249189)
• All Android licenses accepted.

[√] Chrome - develop for the web
• Chrome at C:\Program Files\Google\Chrome\Application\chrome.exe

[√] Android Studio (version 2020.3)
• Android Studio at C:\Program Files\Android\Android Studio
• Flutter plugin can be installed from:
https://plugins.jetbrains.com/plugin/9212-flutter
• Dart plugin can be installed from:
https://plugins.jetbrains.com/plugin/6351-dart
• Java version OpenJDK Runtime Environment (build 11.0.10+0-b96-7249189)

[√] IntelliJ IDEA Ultimate Edition (version 2020.3)
• IntelliJ at C:\Program Files\JetBrains\IntelliJ IDEA 2020.3
• Flutter plugin can be installed from:
https://plugins.jetbrains.com/plugin/9212-flutter
• Dart plugin can be installed from:
https://plugins.jetbrains.com/plugin/6351-dart

[√] VS Code (version 1.62.2)
• VS Code at C:\Users\user\AppData\Local\Programs\Microsoft VS Code
• Flutter extension version 3.28.0

[√] Connected device (1 available)
• Chrome (web) • chrome • web-javascript • Google Chrome 95.0.4638.69

• No issues found!

</details>


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