extension method widening a parameter should not be a breaking change

[dcharkes]

Describe the bug

{
  "breakingChanges": {
    "label": "BREAKING CHANGES",
    "children": [
      {
        "label": "Class BuildOutputBuilderAddDataAssetsDirectories",
        "children": [
          {
            "label": "Method addDataAssetDirectories",
            "children": [
              {
                "changeDescription": "Type of parameter \"input\" changed. BuildInput -> HookInput",
                "changeCode": "CE08",
                "isBreaking": true,
                "type": "major"
              }
            ]
          }
        ]
      }
    ]
  }
}

final class BuildInput extends HookInput {

extension BuildOutputBuilderAddDataAssetsDirectories on BuildOutputBuilder {

Extensions cannot be implemented, so widening a parameter type should be a non-breaking change.

Actual and Expected behavior
Not breaking change.

System info (please complete the following information):

• dart_apitool version: 8654b76

Additional context
https://github.com/dart-lang/native/actions/runs/18614286356/job/53076701689?pr=2712