Fix buggy code examples for ReflectionParameter::getAttributes (#4549)

- Fix calls to non-existent `getParameter` method of `ReflectionFunction`.
- Add missing `Red` attribute class definition implementing `Color`.

Author: daniil-berg

reference/reflection/reflectionparameter/getattributes.xml

@@ -57,7 +57,7 @@ function fruitBasket(
 ) { }
 
 $reflection = new ReflectionFunction('fruitBasket');
-$parameter = $reflection->getParameter('apple');
+$parameter = $reflection->getParameters()[0];
 $attributes = $parameter->getAttributes();
 print_r(array_map(fn($attribute) => $attribute->getName(), $attributes));
 ?>
@@ -96,7 +96,7 @@ function fruitBasket(
 ) { }
 
 $reflection = new ReflectionFunction('fruitBasket');
-$parameter = $reflection->getParameter('apple');
+$parameter = $reflection->getParameters()[0];
 $attributes = $parameter->getAttributes('Fruit');
 print_r(array_map(fn($attribute) => $attribute->getName(), $attributes));
 ?>
@@ -126,14 +126,18 @@ interface Color {
 class Fruit {
 }
 
+#[Attribute]
+class Red implements Color {
+}
+
 function fruitBasket(
    #[Fruit]
    #[Red]
    string $apple
 ) { }
 
 $reflection = new ReflectionFunction('fruitBasket');
-$parameter = $reflection->getParameter('apple');
+$parameter = $reflection->getParameters()[0];
 $attributes = $parameter->getAttributes('Color', ReflectionAttribute::IS_INSTANCEOF);
 print_r(array_map(fn($attribute) => $attribute->getName(), $attributes));
 ?>