When fetching with body from the request 'Content-Length' is missing.

[notorca]

Test script. Request sent to the http://127.0.0.1:8000/foo is chunked.

async fetch(
	request: Request,
	env: Env,
	ctx: ExecutionContext
): Promise<Response> {
	console.log(`Length: ${request.headers.get('Content-Length')}`)
	await fetch("http://127.0.0.1:8000/foo", { method: 'POST', body: request.body! })
	return new Response("Hello World!");
}