[8.x] [Discover] Unskip _sidebar tests for MKI testing (elastic#202133)…

… (elastic#202633)

# Backport

This will backport the following commits from `main` to `8.x`:
- [[Discover] Unskip _sidebar tests for MKI testing
(elastic#202133)](elastic#202133)

<!--- Backport version: 8.9.8 -->

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

<!--BACKPORT [{"author":{"name":"Matthias
Wilhelm","email":"[email protected]"},"sourceCommit":{"committedDate":"2024-12-03T05:17:39Z","message":"[Discover]
Unskip _sidebar tests for MKI testing
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Unskip _sidebar tests for MKI testing
(elastic#202133)","sha":"d1c2e04912714c30e04f3790ed03ba5b5d154061"}},"sourceBranch":"main","suggestedTargetBranches":[],"targetPullRequestStates":[{"branch":"main","label":"v9.0.0","labelRegex":"^v9.0.0$","isSourceBranch":true,"state":"MERGED","url":"https://github.com/elastic/kibana/pull/202133","number":202133,"mergeCommit":{"message":"[Discover]
Unskip _sidebar tests for MKI testing
(elastic#202133)","sha":"d1c2e04912714c30e04f3790ed03ba5b5d154061"}}]}]
BACKPORT-->