Compute SHA in a separate step

.gitea/workflows/docker.yml

@@ -18,6 +18,10 @@ jobs:
           username: ${{ secrets.REGISTRY_USER }}
           password: ${{ secrets.REGISTRY_PASSWORD }}
 
+      - name: Set SHORT_SHA
+        id: vars
+        run: echo "short_sha=${GITHUB_SHA::5}" >> "$GITHUB_OUTPUT"
+
       - name: Set up Docker Buildx
         uses: docker/setup-buildx-action@v3
 
@@ -27,12 +31,10 @@ jobs:
           context: .
           push: true
           platforms: linux/amd64,linux/arm64
-
           build-args: |
-            BUILD_IDENTIFIER=${{ github.sha.substring(0, 5) }}
-
+            BUILD_IDENTIFIER=${{ steps.vars.outputs.short_sha }}
           tags: |
-            gitea.spilum.net/spilum.net/mtf-nlp:${{ github.ref_name }}-${{ github.sha.substring(0, 5) }}
+            gitea.spilum.net/spilum.net/mtf-nlp:${{ github.ref_name }}-${{ steps.vars.outputs.short_sha }}
             gitea.spilum.net/spilum.net/mtf-nlp:${{ github.ref_name }}-latest
 
       - name: Log out from registry