fix github sha ref

Author: johannes94

.github/workflows/multicluster-e2e.yaml

@@ -46,7 +46,7 @@ jobs:
       - name: Set commit short ref
         id: commit-ref
         # did not use git rev-parse here because it requires a checkout before
-        run: echo "GIT_SHORT_REF=$(echo ${{ env.GITHUB_SHA }} | cut -c 7)" >> "$GITHUB_OUTPUT"
+        run: echo "GIT_SHORT_REF=$(echo ${{ github.sha }} | cut -c 7)" >> "$GITHUB_OUTPUT"
       - name: Create cluster
         uses: stackrox/actions/infra/create-cluster@v1
         with: