[UII] Fix unifiedSearch mock in SearchBar jest test (elastic#192211)

## Summary

Resolves elastic#181510. Fixes missing method in the mocked `unifiedSearch`
dependency that was causing flaky test failures.

(cherry picked from commit 24e1b67)

x-pack/plugins/fleet/public/applications/fleet/components/search_bar.test.tsx

@@ -114,6 +114,7 @@ jest.mock('../hooks', () => {
               },
             },
           ]),
+          hasQuerySuggestions: jest.fn().mockReturnValue(true),
         },
         ui: {
           IndexPatternSelect: jest.fn(),