[Backport 2.x] [Fix FuzzyFilterPostingsFormatTests] Suppress sys out checks for test case

[opensearch-trigger-bot]

Backport 3e8e116 from #13188.

[github-actions]

Compatibility status:

Checks if related components are compatible with change 71f9d08

Incompatible components

Skipped components

Compatible components

Compatible components: [https://github.com/opensearch-project/custom-codecs.git, https://github.com/opensearch-project/asynchronous-search.git, https://github.com/opensearch-project/performance-analyzer-rca.git, https://github.com/opensearch-project/flow-framework.git, https://github.com/opensearch-project/cross-cluster-replication.git, https://github.com/opensearch-project/job-scheduler.git, https://github.com/opensearch-project/reporting.git, https://github.com/opensearch-project/security.git, https://github.com/opensearch-project/neural-search.git, https://github.com/opensearch-project/geospatial.git, https://github.com/opensearch-project/common-utils.git, https://github.com/opensearch-project/security-analytics.git, https://github.com/opensearch-project/k-nn.git, https://github.com/opensearch-project/notifications.git, https://github.com/opensearch-project/anomaly-detection.git, https://github.com/opensearch-project/performance-analyzer.git, https://github.com/opensearch-project/observability.git, https://github.com/opensearch-project/ml-commons.git, https://github.com/opensearch-project/index-management.git, https://github.com/opensearch-project/alerting.git, https://github.com/opensearch-project/sql.git]

[github-actions]

❕ Gradle check result for 71f9d08: UNSTABLE

• TEST FAILURES:

      1 org.opensearch.backwards.MixedClusterClientYamlTestSuiteIT.test {p0=indices.get_field_mapping/20_missing_field/Return empty object if field doesn't exist, but index does}

Please review all flaky tests that succeeded after retry and create an issue if one does not already exist to track the flaky failure.