fix: cast vi.fn() mock to satisfy bun-types fetch type (#571)

src/channels/bluesky.test.ts

@@ -24,7 +24,7 @@ describe('BlueskyAdapter', () => {
   const originalFetch = globalThis.fetch;
 
   beforeEach(() => {
-    globalThis.fetch = vi.fn();
+    globalThis.fetch = vi.fn() as unknown as typeof fetch;
   });
 
   afterEach(() => {