Apply suggestion from @mmwinther

Co-authored-by: Miles Mason Winther <42948872+mmwinther@users.noreply.github.com>

Author: Jorgen-5

src/datadoc/datadoc-json-schema.json

@@ -108,7 +108,7 @@
                         "title": "Use restriction date",
                         "description": "Use restriction date, eg. the date (deadline) for when data must be deleted/anonymised.",
                         "type": "string",
-                        "format": "date-time"
+                        "format": "date"
                     }
                 }
             }