[BUG] Add plugin doesn't add content to generated schema file

[LongLiveCHIEF]

Describe the bug
Using the add option to modify the schema.generated.graphqls file fails to add the desired content
to the file.

To Reproduce

// codegen.ts
{
  generates: {
    'src/schema': defineConfig({
      add: {
        './schema.generated.graphql': { content: '/* eslint-disable */' },
      },
    })
  }
}

Expected behavior
Expected /* eslint-disable */ to be inserted at top of generated file

Screenshots
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Versions

• OS: MacOS M4
• OS Version: Tahoe 26.2
• @eddeee888/gcg-typescript-resolver-files

Additional context
Add any other context about the problem here.