[8.19] fix(slo): purge data test (elastic#219389) (elastic#219416)

# Backport

This will backport the following commits from `main` to `8.19`:
- [fix(slo): purge data test
(elastic#219389)](elastic#219389)

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

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

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purge data test (elastic#219389)\n\n## Summary\n\nThis PR addresses an issue
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BACKPORT-->

Co-authored-by: Kevin Delemme <[email protected]>

Author: kibanamachine

x-pack/solutions/observability/plugins/slo/server/services/purge_rollup_data.test.ts

@@ -19,6 +19,8 @@ describe('purge rollup data', () => {
   let mockEsClient: jest.Mocked<ElasticsearchClient>;
   let purgeRollupData: BulkPurgeRollupData;
 
+  jest.useFakeTimers().setSystemTime(new Date('2025-04-24'));
+
   beforeEach(() => {
     mockRepository = createSLORepositoryMock();
     mockEsClient = elasticsearchServiceMock.createElasticsearchClient();