Fix JSON schema to allow $schema

Signed-off-by: Michał Górny <mgorny@quansight.com>

Author: mgorny

peps/pep-0825/variant-schema-0.0.1.json

@@ -5,6 +5,10 @@
   "description": "The format for variant metadata (variant.json) and index-level metadata ({name}-{version}-variants.json)",
   "type": "object",
   "properties": {
+    "$schema": {
+      "description": "JSON schema URL",
+      "type": "string"
+    },
     "default-priorities": {
       "description": "Default priorities for ordering variants",
       "type": "object",
@@ -105,6 +109,7 @@
     }
   },
   "required": [
+    "$schema",
     "default-priorities",
     "variants"
   ],