chore: adjust psalm config

Signed-off-by: Ferdinand Thiessen <opensource@fthiessen.de>

Author: susnux

psalm.xml

@@ -5,6 +5,7 @@
 	findUnusedCode="false"
 	resolveFromConfigFile="true"
 	totallyTyped="true"
+	phpVersion="8.1"
 	xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
 	xmlns="https://getpsalm.org/schema/config"
 	xsi:schemaLocation="https://getpsalm.org/schema/config vendor-bin/psalm/vendor/vimeo/psalm/config.xsd"