chore(deps): truncate Dependabot PR bodies to the Signed-off-by line only and skip the remainder

[jenstroeger]

Assuming we have at least one commit in a Dependabot PR then we grab that one/first commit:

> gh pr view 1116 --json commits
{
  "commits": [
    {
      "authoredDate": "2026-04-08T05:11:37Z",
      "authors": [
        {
          "email": "49699333+dependabot[bot]@users.noreply.github.com",
          "id": "MDM6Qm90NDk2OTkzMzM=",
          "login": "dependabot[bot]",
          "name": "dependabot[bot]"
        }
      ],
      "committedDate": "2026-04-08T05:11:37Z",
      "messageBody": "Bumps [pytest-env](https://github.com/pytest-dev/pytest-env) from 1.2.0 to 1.6.0.\n- [Release notes](https://github.com/pytest-dev/pytest-env/releases)\n- [Commits](https://github.com/pytest-dev/pytest-env/compare/1.2.0...1.6.0)\n\n---\nupdated-dependencies:\n- dependency-name: pytest-env\n  dependency-version: 1.6.0\n  dependency-type: direct:development\n  update-type: version-update:semver-minor\n...\n\nSigned-off-by: dependabot[bot] <support@github.com>",
      "messageHeadline": "chore(deps-dev): bump pytest-env from 1.2.0 to 1.6.0",
      "oid": "bbd0f701e20b7fc6ceab3091fc986a7d25159978"
    }
  ]
}

And from that we can filter out the last line of the commit body:

> gh pr view 1116 --json commits --jq .commits[0].messageBody | grep Signed-off-by
Signed-off-by: dependabot[bot] <support@github.com>

And that line becomes the new body of the squashed & merged PR commit. That’s probably much better to read in a git log than this commit 810123f 🤓