fix: don't report failed network requests as JavaScript errors (#38732)

On the issue ref popup, when the user clicks the link while fetch is
loading, the page will briefly render a network error message before
loading the next page. Suppress unnecessary network errors.

web_src/js/modules/errors.ts

@@ -1,5 +1,6 @@
 // keep this file lightweight, it's imported into IIFE chunk in bootstrap
 import {html} from '../utils/html.ts';
+import isNetworkError from 'is-network-error';
 import type {Intent} from '../types.ts';
 
 /** Extract a message string from an unknown caught value. */
@@ -66,6 +67,10 @@ export function processWindowErrorEvent({error, reason, message, type, filename,
     if (window.config.runModeIsProd) return;
   }
 
+  // Don't show network errors, happens on ref-issue when clicking on the
+  // issue link while the fetch request is still running.
+  if (isNetworkError(err)) return;
+
   // Filter out errors from browser extensions or other non-Gitea scripts.
   if (!isGiteaError(filename ?? '', err?.stack ?? '')) return;