LibWeb: Set max-values for display CSS property

Author: https://github.com/emilitzerjo
Commit: b74940ffb7
Pull-request: https://github.com/SerenityOS/serenity/pull/18524
Reviewed-by: https://github.com/AtkinsSJ
Reviewed-by: https://github.com/nico

Userland/Libraries/LibWeb/CSS/Properties.json

@@ -600,6 +600,7 @@
   "display": {
     "inherited": false,
     "initial": "inline",
+    "max-values": 3,
     "valid-identifiers": [
       "block",
       "contents",