release: allow git checkout ref from triggering event, not always main

if we want to publish on branches then we need to checkout from the branch
we run the publish action on, pinning this to main means it will always publish
from main and no branch publish is ever possible

Author: mikehardy

.github/workflows/publish.yml

@@ -15,7 +15,6 @@ jobs:
     steps:
       - uses: actions/checkout@v6
         with:
-          ref: 'main'
           fetch-depth: 0
           # Repository admin required to evade PR+checks branch protection
           token: ${{ secrets.GH_TOKEN }}