ci: w3.org missed the certifcate date

Author: ktomk

.github/workflows/validate.yml

@@ -28,7 +28,7 @@ jobs:
         run: sudo apt-get install --no-install-recommends -y libxml2-utils
 
       - name: Retrieve XML Schema
-        run: curl -O https://www.w3.org/2012/04/XMLSchema.xsd
+        run: curl -kO https://www.w3.org/2012/04/XMLSchema.xsd
 
       # Show XML violations inline in the file diff.
       # @link https://github.com/marketplace/actions/xmllint-problem-matcher