bug: experimentalDts generates .d.ts with syntax errors

[maxpatiiuk]

This might be a @microsoft/api-extractor bug, but not sure so opening it here first.

Given this source code:

type A = '';
export declare namespace h {
  export type { A as B };
}
export const a: A = '';

The output dist/_tsup-dts-rollup.d.ts contains a syntax error:

export declare namespace h {
    export declare type { A as B };
}

should instead be:

export declare namespace h {
    export type { A as B };
}

Repository with a minimal reproduction

(note I am using namespaces because I need to provide jsx runtime typings)

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