FIX - Failing test: Stateful Observability - Deployment-agnostic Feature Flag API Integration Tests.x-pack/test/api_integration/deployment_agnostic/apis/observability/alerting/synthetics/custom_status_rule·ts - Stateful Observability feature flag testing - Deployment-agnostic API integration tests SyntheticsCustomStatusRule "after all" hook in "SyntheticsCustomStatusRule" (#225090)

## Summary

It fixes #224778
✅ Falky test runner
https://buildkite.com/elastic/kibana-flaky-test-suite-runner/builds/8441
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Author: fkanout

x-pack/test/api_integration/deployment_agnostic/apis/observability/alerting/synthetics/custom_status_rule.ts

@@ -73,6 +73,7 @@ export default function ({ getService }: DeploymentAgnosticFtrProviderContext) {
       await esClient.deleteByQuery({
         index: SYNTHETICS_RULE_ALERT_INDEX,
         query: { match_all: {} },
+        conflicts: 'proceed',
       });
     });