Update WordPress core and PHP version in wp-env config

Changed the WordPress core version to 6.9 and updated the PHP version to 8.1 in .wp-env.json for improved compatibility and performance.

Author: mtoensing

.wp-env.json

@@ -1,4 +1,5 @@
 {
-	"phpVersion": "7.0",
-	"plugins": [ "." ]
-}
+  "core": "WordPress/WordPress#6.9",
+  "phpVersion": "8.1",
+  "plugins": [ "." ]
+}