fix(node-fetch): support HeaderInit
fix(node-fetch): support HeaderInit

In previous change to fix the HeadersInit type, I renamed HeaderInit to HeadersInit.

Ref #34382

georgemarshall/DefinitelyTyped,mcliment/DefinitelyTyped,georgemarshall/DefinitelyTyped,markogresak/DefinitelyTyped,borisyankov/DefinitelyTyped,georgemarshall/DefinitelyTyped,borisyankov/DefinitelyTyped,dsebastien/DefinitelyTyped,dsebastien/DefinitelyTyped,georgemarshall/DefinitelyTyped