PR-into-next-branch.yml: only fetch the head commit from both branches

.github/workflows/PR-into-next-version.yml

@@ -32,7 +32,6 @@ jobs:
         uses: actions/checkout@v3
         with:
           ref: ${{ inputs.to-branch }}
-          fetch-depth: 0
 
       # actually merge from the previous branch
       - name: Perform merge from ${{ inputs.from-version }} to ${{ inputs.to-version }}
@@ -41,6 +40,8 @@ jobs:
           git config user.name 'github-actions[bot]'
           git config user.email 'github-actions[bot]@users.noreply.github.com'
           
+          git fetch origin ${{ inputs.from-branch }} --depth=1
+
           # actual merge operation
           git merge --no-ff --message "Merge ${{ inputs.from-branch }}" origin/${{ inputs.from-branch }} -- || ( echo "Merge failed. Please merge manually!" ; exit 1 )