Fix font-variant subfeature spec URL

Author: caugner

css/properties/font-variant.json

@@ -51,7 +51,7 @@
         "css_fonts_shorthand": {
           "__compat": {
             "description": "CSS Fonts Module Level 3 shorthand",
-            "spec_url": "https://drafts.csswg.org/css-fonts-3/#font-variant-prop",
+            "spec_url": "https://drafts.csswg.org/css-fonts/#font-variant-prop",
             "tags": [
               "web-features:font-variant"
             ],