Fix return type deprecations

Author: tbredillet

reference/forms/types/options/choice_filter.rst.inc

@@ -18,7 +18,7 @@ define a callable that takes each choice as the only argument and must return
 
     class AddressType extends AbstractType
     {
-        public function configureOptions(OptionsResolver $resolver)
+        public function configureOptions(OptionsResolver $resolver): void
         {
             $resolver
                 ->setDefaults([

reference/forms/types/options/choice_loader.rst.inc

@@ -57,7 +57,7 @@ better performance::
             return ChoiceType::class;
         }
 
-        public function configureOptions(OptionsResolver $resolver)
+        public function configureOptions(OptionsResolver $resolver): void
         {
             $resolver->setDefaults([
                 // the example below will create a CallbackChoiceLoader from the callable

reference/forms/types/options/error_mapping.rst.inc

@@ -13,7 +13,7 @@ of the form.
 With customized error mapping, you can do better: map the error to the city
 field so that it displays above it::
 
-    public function configureOptions(OptionsResolver $resolver)
+    public function configureOptions(OptionsResolver $resolver): void
     {
         $resolver->setDefaults([
             'error_mapping' => [

reference/forms/types/options/validation_groups.rst.inc

@@ -11,7 +11,7 @@ For ``null`` the validator will just use the ``Default`` group.
 If you specify the groups as an array or string they will be used by the
 validator as they are::
 
-    public function configureOptions(OptionsResolver $resolver)
+    public function configureOptions(OptionsResolver $resolver): void
     {
         $resolver->setDefaults([
             'validation_groups' => 'Registration',
@@ -31,7 +31,7 @@ the option. Symfony will then pass the form when calling it::
     use Symfony\Component\OptionsResolver\OptionsResolver;
 
     // ...
-    public function configureOptions(OptionsResolver $resolver)
+    public function configureOptions(OptionsResolver $resolver): void
     {
         $resolver->setDefaults([
             'validation_groups' => function (FormInterface $form): array {
@@ -69,7 +69,7 @@ Here's an example::
     class MyType extends AbstractType
     {
         // ...
-        public function configureOptions(OptionsResolver $resolver)
+        public function configureOptions(OptionsResolver $resolver): void
         {
             $resolver->setDefaults([
                 'validation_groups' => new GroupSequence(['First', 'Second']),