Update validate-assets job in CI workflow

Author: mattt

.github/workflows/ci.yml

@@ -176,9 +176,9 @@ jobs:
       - name: Test assets
         run: |
           cd .node
-          OLD=`cksum ../Resources/all.min.css`
+          OLD=`cksum ../Sources/swift-doc/Generated/CSS.swift`
           npm run build
-          NEW=`cksum ../Resources/all.min.css`
+          NEW=`cksum ../Sources/swift-doc/Generated/CSS.swift`
           if [[ "$OLD" != "$NEW" ]]; then
             echo "Regenerated assets differ from committed version"
             exit -1