fix: guard windows nightly cache purge secrets

Author: PerishCode

.github/workflows/desktop-nightly.yml

@@ -170,7 +170,7 @@ jobs:
           aws s3 cp "apps/desktop/channel-artifacts-win/${{ steps.artifacts.outputs.manifest_file }}" "s3://nexu-desktop-releases/$prefix/${{ steps.artifacts.outputs.manifest_file }}" --no-progress
 
       - name: Purge Windows latest CDN artifacts
-        if: env.CLOUDFLARE_ZONE_ID != ''
+        if: secrets.CLOUDFLARE_ZONE_ID != '' && secrets.CLOUDFLARE_PURGE_API_TOKEN != ''
         env:
           CLOUDFLARE_ZONE_ID: ${{ secrets.CLOUDFLARE_ZONE_ID }}
           CLOUDFLARE_PURGE_API_TOKEN: ${{ secrets.CLOUDFLARE_PURGE_API_TOKEN }}