Update Psalm configuration to use phpVersion attribute

Author: lennartdohmann

psalm.xml

@@ -6,8 +6,8 @@
     xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
     xmlns="https://getpsalm.org/schema/config"
     xsi:schemaLocation="https://getpsalm.org/schema/config vendor/vimeo/psalm/config.xsd"
+    phpVersion="8.1"
 >
-    <phpVersion>8.1</phpVersion>
     <projectFiles>
         <directory name="lib" />
         <ignoreFiles>