remotes.schema.json: fix typo - 'artifacts' mistyped as 'atrifacts'

remotes.schema.json

@@ -39,7 +39,7 @@
                       "type": "string",
                       "description": "Ardupilot version number for that release"
                     },
-                    "ap_build_atrifacts_url": {
+                    "ap_build_artifacts_url": {
                       "type": "string",
                       "description": "url to build artifacts at AP firmware server to fetch features.txt"
                     },