docs: add release notes for v1.1.51

Author: github-actions[bot]

release_notes/v1.1.51.md

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+## [1.1.51](https://github.com/NHSDigital/eps-FHIR-validator-lambda/compare/v1.1.50...v1.1.51) (2026-02-19)
+
+
+### Upgrade
+
+* [dependabot] - bump NHSDigital/eps-common-workflows/.github/workflows/dependabot-auto-approve-and-merge.yml from 5.3.12 to 5.4.1 (#436) ([9cb17d2](https://github.com/NHSDigital/eps-FHIR-validator-lambda/commit/9cb17d2164655da202f834d45a7e266f67a16ee5))
+* [dependabot] - bump NHSDigital/eps-common-workflows/.github/workflows/pr_title_check.yml from 5.3.12 to 5.4.1 (#437) ([37b1342](https://github.com/NHSDigital/eps-FHIR-validator-lambda/commit/37b1342fda74fa0b387d67b4c0fdc4629f2563df))
+* [dependabot] - bump NHSDigital/eps-common-workflows/.github/workflows/quality-checks.yml from 5.3.12 to 5.4.1 (#440) ([f591abe](https://github.com/NHSDigital/eps-FHIR-validator-lambda/commit/f591abe1eadace0fb59cb694f94d6870cd499480))
+* [dependabot] - bump NHSDigital/eps-common-workflows/.github/workflows/tag-release.yml from 5.3.12 to 5.4.1 (#438) ([513ba35](https://github.com/NHSDigital/eps-FHIR-validator-lambda/commit/513ba3531f71c2bdfecd9e6b8f8960663d472b73))
+
+
+
+
+## Info
+[Release workflow run](https://github.com/NHSDigital/eps-FHIR-validator-lambda/actions/runs/22173742878) - Workflow ID: 22173742878
+
+It was initialized by [anthony-nhs](https://github.com/anthony-nhs)
+
+