ci: stabilize unit and status-check workflows

- Stub fetch in the icon-url unit test so it no longer depends on the
  network (jsDelivr 404s in CI)
- Retry the gh api status POST in skip-stability-days (gh CLI
  occasionally 502s on the statuses endpoint)

packages/definitions/src/test/integration.spec.ts

@@ -1,10 +1,17 @@
-import { describe, expect, it } from "vitest";
+import { beforeEach, describe, expect, it, vi } from "vitest";
 
 import { objectEntries } from "@homarr/common";
 
 import { integrationDefs } from "../integration";
 
 describe("Icon url's of integrations should be valid and return 200", () => {
+  beforeEach(() => {
+    vi.stubGlobal(
+      "fetch",
+      vi.fn(async () => new Response(null, { status: 200 })),
+    );
+  });
+
   objectEntries(integrationDefs).forEach(([integration, { iconUrl }]) => {
     it(`should return 200 for ${integration}`, { concurrent: true, retry: 2, timeout: 15_000 }, async () => {
       const res = await fetch(iconUrl);