Update css/types/attr.json

Co-authored-by: Claas Augner <495429+caugner@users.noreply.github.com>

Author: dletorey

css/types/attr.json

@@ -83,7 +83,8 @@
         "namespaces": {
           "__compat": {
             "description": "namespaced attributes",
-            "spec_url": "https://drafts.csswg.org/css-values-5/#typedef-attr-name",
+            "mdn_url": "https://developer.mozilla.org/docs/Web/CSS/Reference/Values/attr#namespaces",
+            "spec_url": "https://drafts.csswg.org/css-values-5/#typedef-attr-name:~:text=namespaced%20attributes",
             "tags": [
               "web-features:attr"
             ],