fix: detection of CORS preflight requests for skipCorsPreflight option

[Luzefiru]

It seems like this checker was checking the incorrect request header. Cross-Origin-Request-Method doesn't seem to be included in CORS preflight requests, so I changed it to Access-Control-Request-Method and the skipCorsPreflight works now.

/**
 * Checks if the request is a CORS preflight request
 */
function isCORSPreflightRequest(request: Request) {
  return (
    request.method === "OPTIONS" &&
    request.headers.has("Origin") &&
-    request.headers.has("Cross-Origin-Request-Method")
+    request.headers.has("Access-Control-Request-Method")
  )
}

[eelkevdbos]

Thanks, this looks good!