chore: use bot identity and SSH signing for commits

[TomerFi]

Summary

• Switch git identity from github.actor to github-actions[bot] (ID 41898282)
• Add SSH commit signing using SIGNING_KEY secret
• Updates both release.yml and test_run.yml (update_readme job)

Changes

Identity

git config user.name "github-actions[bot]"
git config user.email "41898282+github-actions[bot]@users.noreply.github.com"

SSH Signing

- name: Setup SSH signing
  run: |
    mkdir -p ~/.ssh
    echo "${{ secrets.SIGNING_KEY }}" > ~/.ssh/signing_key
    chmod 600 ~/.ssh/signing_key
    git config gpg.format ssh
    git config user.signingkey ~/.ssh/signing_key
    git config commit.gpgsign true

Prerequisites

1. Add public SSH key to GitHub account as signing key
2. Add SIGNING_KEY secret to release and update-docs environments