[Docs] Add known issue about upgrade error (elastic#207629)

## Summary

Adding elastic#187254 as a known issue to the 8.10.0 release notes + all
subsequent versions.

See [slack
thread](https://elastic.slack.com/archives/CED7QCL3E/p1737476287242609)
for details.

Closes:
[elastic#622](https://github.com/orgs/elastic/projects/1232/views/54?pane=issue&itemId=94643452&issue=elastic%7Cplatform-docs-team%7C622)

(cherry picked from commit c17f45d)

# Conflicts:
#	docs/CHANGELOG.asciidoc

docs/CHANGELOG.asciidoc

@@ -48,8 +48,8 @@ Review important information about the {kib} 8.x releases.
 
 --
 [[release-notes-8.9.2]]
-== {kib} 8.9.2
-
+== {kib} 8.9.2 
+21
 Review the following information about the {kib} 8.9.2 release.
 
 [float]