CI: avoid deprecated set-output method

Author: uyjulian

.github/workflows/compilation.yml

@@ -31,7 +31,7 @@ jobs:
     
     - name: Get short SHA
       id: slug
-      run: echo "sha8=$(echo ${GITHUB_SHA} | cut -c1-8)" >> $GITHUB_OUTPUT
+      run: printf '%s\n' "sha8=$(printf '%s\n' ${GITHUB_SHA} | cut -c1-8)" >> $GITHUB_OUTPUT
 
     - name: Upload artifacts
       if: ${{ success() }}