📝 Update release notes

[skip ci]

Author: github-actions[bot]

docs/en/docs/release-notes.md

@@ -7,6 +7,10 @@ hide:
 
 ## Latest Changes
 
+### Features
+
+* ✨ Replace `dict` by `Mapping` on `HTTPException.headers`. PR [#12997](https://github.com/fastapi/fastapi/pull/12997) by [@rijenkii](https://github.com/rijenkii).
+
 ### Internal
 
 * 🔧 Configure `test` workflow to run tests with `inline-snapshot=review`. PR [#14876](https://github.com/fastapi/fastapi/pull/14876) by [@YuriiMotov](https://github.com/YuriiMotov).