fix: make Attic push non-fatal in docker-build-nix

docker-build-nix/action.yaml

@@ -64,6 +64,7 @@ runs:
     - name: Push build artifacts to Attic cache
       shell: bash
       if: env.ATTIC_TOKEN != ''
+      continue-on-error: true
       env:
         ATTIC_TOKEN: ${{ env.ATTIC_TOKEN }}
       run: |
@@ -75,8 +76,8 @@ runs:
         token = "${ATTIC_TOKEN}"
         EOF
 
-        # Push entire closure to cache
-        attic push "${{ inputs.cache-name }}" ./result
+        # Push entire closure to cache (don't fail if this fails)
+        attic push "${{ inputs.cache-name }}" ./result || echo "Warning: Failed to push to Attic cache, continuing anyway"
 
     - name: Load image into Docker
       shell: bash