Fix Docker build by properly handling BUILD_DATE environment variable

Author: JohanDevl

.github/workflows/docker-build.yml

@@ -73,6 +73,10 @@ jobs:
           username: ${{ github.actor }}
           password: ${{ secrets.GITHUB_TOKEN }}
 
+      - name: Set build date
+        id: build_date
+        run: echo "BUILD_DATE=$(date -u +'%Y-%m-%dT%H:%M:%SZ')" >> $GITHUB_OUTPUT
+
       - name: Build and export Docker image
         uses: docker/build-push-action@v6
         with:
@@ -87,7 +91,7 @@ jobs:
           build-args: |
             VERSION=${{ steps.meta.outputs.version }}
             COMMIT_SHA=${{ github.sha }}
-            BUILD_DATE=$(date -u +'%Y-%m-%dT%H:%M:%SZ')
+            BUILD_DATE=${{ steps.build_date.outputs.BUILD_DATE }}
 
       - name: Scan image for vulnerabilities
         if: github.event_name != 'pull_request'