ci: simplify release PR comment (#449)

Cf. [doc
here](https://github.com/cargo-bins/release-pr?tab=readme-ov-file#inputs)

Author: delehef

.github/workflows/prepare-release.yml

@@ -31,3 +31,5 @@ jobs:
           github-token: ${{ secrets.GITHUB_TOKEN }}
           # Keep all the crates versions in sync
           crate-release-all: true
+          pr-meta-comment: false
+          pr-merge-strategy: "squash"