Upgrade: [dependabot] - bump @middy/http-header-normalizer

Bumps [@middy/http-header-normalizer](https://github.com/middyjs/middy/tree/HEAD/packages/http-header-normalizer) from 5.5.1 to 6.0.0.
- [Release notes](https://github.com/middyjs/middy/releases)
- [Changelog](https://github.com/middyjs/middy/blob/main/docs/CHANGELOG.md)
- [Commits](https://github.com/middyjs/middy/commits/6.0.0/packages/http-header-normalizer)

---
updated-dependencies:
- dependency-name: "@middy/http-header-normalizer"
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

package-lock.json

@@ -19,7 +19,7 @@
     "@aws-lambda-powertools/parameters": "^2.11.0",
     "@aws-sdk/client-secrets-manager": "^3.696.0",
     "@middy/core": "^5.5.1",
-    "@middy/http-header-normalizer": "^5.5.1",
+    "@middy/http-header-normalizer": "^6.0.0",
     "@middy/input-output-logger": "^5.5.1",
     "@nhs/fhir-middy-error-handler": "^2.1.11",
     "@NHSDigital/eps-spine-client": "^2.1.10",