add missing closing dropdown tag (#8885) (#8888)

(cherry picked from commit 266bf68)

Author: rhr323

docs/release-notes/known-issues.md

@@ -57,6 +57,7 @@ spec:
             - name: FLEET_FORCE
               value: "true"
 ```
+:::
 
 ## 3.1.0 [elastic-cloud-kubernetes-310-known-issues]