docs: add release notes for v5.6.1

Author: github-actions[bot]

release_notes/v5.6.1.md

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+## [5.6.1](https://github.com/NHSDigital/eps-common-workflows/compare/v5.6.0...v5.6.1) (2026-03-05)
+
+
+### Fix
+
+* [AEA-0000] - Always run valid trivy scans even if a previous scan failed, so that all vulnerabilities are identified at once. Shorten feedback cycle for vulnerabilities across multiple scans. (#78) ([d116ba9](https://github.com/NHSDigital/eps-common-workflows/commit/d116ba935f2a9544c7bcc6dc37ea997fada6e780))
+
+## Info
+[Release workflow run](https://github.com/NHSDigital/eps-common-workflows/actions/runs/22727356777) - Workflow ID: 22727356777
+
+It was initialized by [connoravo-nhs](https://github.com/connoravo-nhs)
+
+