ci(build): use version variable

Author: MrMarble

.github/workflows/build.yml

@@ -35,6 +35,10 @@ jobs:
     steps:
       - uses: actions/checkout@v4
 
+      - name: Extract version
+        run: |
+          echo "version=$(git describe --tags --dirty --always --abbrev=12)" >> "$GITHUB_ENV"
+
       - name: Set up Docker Buildx
         uses: docker/setup-buildx-action@f95db51fddba0c2d1ec667646a06c2ce06100226 # v3.0.0
 
@@ -50,7 +54,7 @@ jobs:
         with:
           context: .
           build-args: |
-            VERSION=$(git describe --tags --dirty --always --abbrev=12)
+            VERSION=$version
           push: false
           load: true
           tags: rootfsimage