[8.x] fix `Cannot read properties of null (reading 'closed')` when chrome is remounted (elastic#210075) (elastic#210100)

# Backport

This will backport the following commits from `main` to `8.x`:
- [fix `Cannot read properties of null (reading
'closed')` when chrome is remounted
(elastic#210075)](elastic#210075)

<!--- Backport version: 9.4.3 -->

### Questions ?
Please refer to the [Backport tool
documentation](https://github.com/sqren/backport)

<!--BACKPORT [{"author":{"name":"Anton
Dosov","email":"[email protected]"},"sourceCommit":{"committedDate":"2025-02-06T19:02:59Z","message":"fix
`Cannot read properties of null (reading 'closed')` when chrome is
remounted
(elastic#210075)","sha":"cd398d939462ebeb73f05c4fdd1d88db349eacf8","branchLabelMapping":{"^v9.1.0$":"main","^v8.19.0$":"8.x","^v(\\d+).(\\d+).\\d+$":"$1.$2"}},"sourcePullRequest":{"labels":["release_note:skip","backport:prev-minor","backport:prev-major","v9.1.0"],"title":"fix
`Cannot read properties of null (reading 'closed')` when chrome is
remounted
","number":210075,"url":"https://github.com/elastic/kibana/pull/210075","mergeCommit":{"message":"fix
`Cannot read properties of null (reading 'closed')` when chrome is
remounted
(elastic#210075)","sha":"cd398d939462ebeb73f05c4fdd1d88db349eacf8"}},"sourceBranch":"main","suggestedTargetBranches":[],"targetPullRequestStates":[{"branch":"main","label":"v9.1.0","branchLabelMappingKey":"^v9.1.0$","isSourceBranch":true,"state":"MERGED","url":"https://github.com/elastic/kibana/pull/210075","number":210075,"mergeCommit":{"message":"fix
`Cannot read properties of null (reading 'closed')` when chrome is
remounted
(elastic#210075)","sha":"cd398d939462ebeb73f05c4fdd1d88db349eacf8"}}]}]
BACKPORT-->

Co-authored-by: Anton Dosov <[email protected]>

Author: kibanamachine

x-pack/solutions/observability/plugins/observability_ai_assistant_app/public/hooks/is_nav_control_visible.tsx

@@ -55,7 +55,7 @@ export function useIsNavControlVisible({ coreStart, pluginsStart }: UseIsNavCont
       },
     });
 
-    return appSubscription.unsubscribe;
+    return () => appSubscription.unsubscribe();
   }, [currentAppId$, applications$, aiAssistantManagementSelection.aiAssistantType$]);
 
   return {