test(defaults): update default PHP version to 8.4

Author: EtienneM

test/defaults

@@ -18,7 +18,7 @@ default_composer["scalingo-22"]="2.8."
 latest_composer["scalingo-22"]="2.8.11"
 
 # Defaults for scalingo-24:
-default_php["scalingo-24"]="8.1."
+default_php["scalingo-24"]="8.4."
 default_nginx["scalingo-24"]="1.28."
 default_composer["scalingo-24"]="2.8."
 latest_composer["scalingo-24"]="2.8.11"