fix(fetch-error-handler): don't treat 304 responses as errors

`Response.ok` is only `true` for a 2xx response, but we don't want to
throw for 304 responses.

this is only a problem for apps that are sending `if-modified-since` or
`if-none-match` headers, which is rare, but happens to be done by
`@apollo/datasource-rest` in `cp-content-pipeline`.

Author: apaleslimghost

packages/fetch-error-handler/lib/create-handler.js

@@ -144,7 +144,8 @@ function createFetchErrorHandler(options = {}) {
 			}
 
 			// If the response isn't OK, we start throwing errors
-			if (!response.ok) {
+			// 304 is considered non-OK by fetch, but we don't consider that an error
+			if (!response.ok && response.status !== 304) {
 				// Parse the response URL so we can use the hostname in error messages
 				let responseHostName = 'unknown';
 				if (typeof response.url === 'string') {