Upgrade the Mergify CLI

The skills follow the latest CLI release. When mergify rejects a command or flag a skill names (unrecognized subcommand, unexpected argument), the installed CLI is probably older than the skill.

1. Compare versions

mergify --version prints the installed version. The release notes give the latest one and the release that added the command. A CLI recent enough to have mergify self-update --check prints both versions.

2. Ask the user

Upgrading replaces a binary on the user's machine: ask before you do it.

3. Upgrade through the channel that installed it