Topic on Extension talk:GeoData/Flow

After patching up to the latest version of Mediawiki (1.38.4) I tried updating my PHP from 7.4 to 8.1 and everything seems to work great... except for one error:

Deprecated: Return type of GeoData\CoordinatesOutput::jsonSerialize() should either be compatible with JsonSerializable::jsonSerialize(): mixed, or the #[\ReturnTypeWillChange] attribute should be used to temporarily suppress the notice in /var/www/my.wiki/public_html/mediawiki-1.38.2/extensions/GeoData/includes/CoordinatesOutput.php on line 141

Does anyone know what's causing this and how to correct it? (Or do I just need to wait a while longer to go up to PHP 8.1?)

1.38 does not support PHP 8.1 yet. Though if you want to manually apply the patch, the 1.39 patch for this issue is in phab:T311919