docs(focusManager): fix duplicate 'event' typo in test comment (#10114)

Remove the duplicated "event" in the test comment of focusManager.test.tsx.

Author: ramong26

packages/query-core/src/__tests__/focusManager.test.tsx

@@ -98,7 +98,7 @@ describe('focusManager', () => {
 
     unsubscribe()
 
-    // Should unsubscribe our event event
+    // Should unsubscribe our event listener once
     expect(unsubscribeSpy).toHaveBeenCalledTimes(1)
 
     handlerSpy.mockRestore()