What does this error message mean?
[10-Mar-2021 23:31:58 America/Chicago] PHP Warning: API call had warnings trying to get remote JsonConfig: warnings={"main":{"*":"Subscribe to the mediawiki-api-announce mailing list at \u003Chttps://lists.wikimedia.org/mailman/listinfo/mediawiki-api-announce\u003E for notice of API deprecations and breaking changes. Use Special:ApiFeatureUsage to see usage of deprecated features by your application."},"revisions":{"*":"Because \"rvslots\" was not specified, a legacy format has been used for the output. This format is deprecated, and in the future the new format will always be used."}}, query={"action":"query","titles":"Data:I18n/Shared Template Warning.tab","prop":"revisions","rvprop":"content","continue":""} [Called from JsonConfig\JCUtils::warn in /extensions/JsonConfig/includes/JCUtils.php at line 54] in /includes/debug/MWDebug.php on line 333