Update release notes

Signed-off-by: Leandro Lucarella <luca-frequenz@llucax.com>

Author: llucax

RELEASE_NOTES.md

@@ -28,6 +28,7 @@ But you might still need to adapt your code:
 
 - The cookiecutter now asks whether a repository is private, defaults that answer from the selected license, and uses it to toggle private-repository workflow behavior, public publishing jobs, and the link to GitHub Discussions in the issue template chooser.
 - All dependencies have been updated in the templates.
+- API projects now ship a dedicated `grpc-migration.yaml` workflow that runs after Dependabot bumps `grpcio`/`grpcio-tools`/`protobuf` and rewrites the matching runtime `>=` floors in `pyproject.toml`.
 
 ## Bug Fixes