Oversized commit messages cause Notify Discord (start) to fail

The Notify Discord (start) job includes the commit message for extra details in the `#builds` channel. Unfortunately if the message is too long, the webhook will simply refuse to post it. This is not caught as an error in GitHub Actions, so the action just proceeds as normal.

case in point: https://github.com/MinecraftForge/GitVersion/actions/runs/13912274029/job/38928786422