await errFn that may be a Promise

This fixes a complaint by a google-internal linter

Release-Notes: skip
Change-Id: I2dd37c1f07b283dd285b7fe5e42efde4097bff93
diff --git a/polygerrit-ui/app/elements/shared/gr-rest-api-interface/gr-rest-apis/gr-rest-api-helper.ts b/polygerrit-ui/app/elements/shared/gr-rest-api-interface/gr-rest-apis/gr-rest-api-helper.ts
index 2de5b5f..8b3e2a6 100644
--- a/polygerrit-ui/app/elements/shared/gr-rest-api-interface/gr-rest-apis/gr-rest-api-helper.ts
+++ b/polygerrit-ui/app/elements/shared/gr-rest-api-interface/gr-rest-apis/gr-rest-api-helper.ts
@@ -533,7 +533,7 @@
     } catch (err) {
       fireNetworkError(err as Error);
       if (req.errFn) {
-        req.errFn.call(undefined, null, err as Error);
+        await req.errFn.call(undefined, null, err as Error);
         xhr = undefined;
       } else {
         throw err;