[9.1] Fix hasNoChanges description comparison (#244521) (#244768)

# Backport

This will backport the following commits from `main` to `9.1`:
- [Fix hasNoChanges description comparison
(#244521)](#244521)

<!--- Backport version: 9.6.6 -->

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

<!--BACKPORT [{"author":{"name":"Krzysztof
Kowalczyk","email":"krzysztof.kowalczyk@elastic.co"},"sourceCommit":{"committedDate":"2025-12-01T13:32:44Z","message":"Fix
hasNoChanges description comparison (#244521)\n\n## Summary\n\nThis PR
fixes a bug where for dashboard listing page, some recent change\nmade
it so a newly created dashboard has description as `undefined`\ninstead
of an empty string, this leads to the content editor flyout\nalways
showing as having changes as the description comparison check\nwouldn't
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hasNoChanges description
comparison","number":244521,"url":"https://github.com/elastic/kibana/pull/244521","mergeCommit":{"message":"Fix
hasNoChanges description comparison (#244521)\n\n## Summary\n\nThis PR
fixes a bug where for dashboard listing page, some recent change\nmade
it so a newly created dashboard has description as `undefined`\ninstead
of an empty string, this leads to the content editor flyout\nalways
showing as having changes as the description comparison check\nwouldn't
work
properly.","sha":"2cb23e19ffaa58eb93928163179df6c1214e3773"}},"sourceBranch":"main","suggestedTargetBranches":[],"targetPullRequestStates":[{"branch":"main","label":"v9.3.0","branchLabelMappingKey":"^v9.3.0$","isSourceBranch":true,"state":"MERGED","url":"https://github.com/elastic/kibana/pull/244521","number":244521,"mergeCommit":{"message":"Fix
hasNoChanges description comparison (#244521)\n\n## Summary\n\nThis PR
fixes a bug where for dashboard listing page, some recent change\nmade
it so a newly created dashboard has description as `undefined`\ninstead
of an empty string, this leads to the content editor flyout\nalways
showing as having changes as the description comparison check\nwouldn't
work properly.","sha":"2cb23e19ffaa58eb93928163179df6c1214e3773"}}]}]
BACKPORT-->

Co-authored-by: Krzysztof Kowalczyk <krzysztof.kowalczyk@elastic.co>

Author: kibanamachine

src/platform/packages/shared/content-management/content_editor/src/components/editor_flyout_content.tsx

@@ -88,9 +88,11 @@ export const ContentEditorFlyoutContent: FC<Props> = ({
       return arr1.every((tag: string, index) => tag === arr2[index]);
     };
 
+    const description = item.description || '';
+
     return (
       item.title === form.title.value &&
-      item.description === form.description.value &&
+      description === form.description.value &&
       compareTags(itemTags, formTags)
     );
   };