Add missing anchors field in top-level of validation config

docs/schema/validation.json

@@ -7,6 +7,7 @@
     "omitted_files": { "$ref": "#/$defs/omitted_files" },
     "not_found": { "$ref": "#/$defs/not_found" },
     "absolute_links": { "$ref": "#/$defs/absolute_links" },
+    "anchors": { "$ref": "#/$defs/anchors" },
     "unrecognized_links": { "$ref": "#/$defs/unrecognized_links" },
     "nav": {
       "title": "validation of navigation",