proxyRequest() doesn't take into account header casing when overriding headers.

[efraimbart]

If a header is sent by the client with one casing and it's overridden with another in proxyRequest they'll both be sent.

h3/src/utils/proxy.ts

Lines 42 to 49 in a3192fb

	// Headers
	const headers = getProxyRequestHeaders(event);
	if (opts.fetchOptions?.headers) {
	Object.assign(headers, opts.fetchOptions.headers);
	}
	if (opts.headers) {
	Object.assign(headers, opts.headers);
	}

[pi0]

Thanks for the report. It will be fixed in the next release.