test: remove unused playSpy variable in player startup test

frontend/src/main.test.ts

@@ -126,7 +126,7 @@ describe("player startup", () => {
       value: vi.fn(() => ""),
       configurable: true,
     });
-    const playSpy = vi.spyOn(video, "play").mockResolvedValue(undefined as any);
+    vi.spyOn(video, "play").mockResolvedValue(undefined as any);
 
     await import("../src/main").then((mod) => mod.initPlayerAndChat(async () => ({ default: HlsMock }) as any));