ci: use more reliable head_sha as checkout ref for release

Author: henri-hulski

.github/workflows/release.yml

@@ -14,7 +14,7 @@ jobs:
       - uses: actions/checkout@v5
         with:
           fetch-depth: 0
-          ref: ${{ github.event.workflow_run.head_branch }}
+          ref: ${{ github.event.workflow_run.head_sha }}
       - uses: actions/setup-node@v6
         with:
           node-version: 22