test: add test case for fetch throwing TypeError on network errors

src/browser/tests/net/fetch.html

@@ -203,3 +203,15 @@
     testing.expectEqual(true, response.body !== null);
   });
 </script>
+
+<script id=error>
+  testing.async(async (restore) => {
+    try {
+      await fetch('http://198.51.100.1:0');
+      testing.expectTrue(false); // force failure
+    } catch (err) {
+      restore();
+      testing.expectTrue(err instanceof TypeError)
+    }
+  });
+</script>

src/browser/webapi/net/Fetch.zig

@@ -193,9 +193,7 @@ fn httpErrorCallback(ctx: *anyopaque, err: anyerror) void {
     defer ls.deinit();
 
     // fetch() must reject with a TypeError on network errors per spec
-    const err_handle = ls.local.isolate.createTypeError("Failed to fetch");
+    ls.toLocal(self._resolver).rejectError("fetch error", .{ .type_error = @errorName(err) });
-    const err_val = js.Value{ .local = ls.local, .handle = err_handle };
-    ls.toLocal(self._resolver).reject("fetch error", err_val);
 }
 
 fn httpShutdownCallback(ctx: *anyopaque) void {