Update validate.yml

Using main validator

Author: glenrobson

.github/workflows/validate.yml

@@ -17,7 +17,7 @@ jobs:
         uses: actions/checkout@v5
 
       - name: Run IIIF validator
-        uses: IIIF/presentation-validator@v4
+        uses: IIIF/presentation-validator@main
         with:
           directory: source/presentation/4.0/example/
-          version: "4.0"
+          version: "4.0"