Fix FormTypeClassValidatorTest on PHPUnit 12.2 (Symfony 8.x CI matrix)

The captureMessages() helper stubbed ConstraintViolationBuilderInterface and
configured its setParameter() method. That method returns `static`, which the
PHPUnit version simple-phpunit pins on the Symfony 8.x matrix (12.2) cannot
configure via createStub() - it throws MethodCannotBeConfiguredException. It
passed locally only because we run PHPUnit 12.5.

Reuse the file's existing concrete ConstraintViolationBuilderStub (real fluent
methods, no mocking) - the same stub the other violation tests in this file
already use and which passes CI. Only the builder changes; the context stub,
which returns the interface (not static), is unaffected.

Author: silverbackdan

tests/Validator/Constraints/FormTypeClassValidatorTest.php

@@ -199,9 +199,10 @@ private function captureMessages(mixed $value, Constraint $constraint, iterable
         $validator = new FormTypeClassValidator($formTypes);
 
         $messages = [];
-        $builder = $this->createStub(ConstraintViolationBuilderInterface::class);
-        $builder->method('setParameter')->willReturn($builder);
-        $builder->method('atPath')->willReturn($builder);
+        // Reuse the concrete stub: ConstraintViolationBuilderInterface's fluent methods return
+        // `static`, which the PHPUnit version pinned by simple-phpunit on the Symfony 8.x matrix
+        // (12.2) cannot mock via createStub() (works on 12.5 locally, fails on CI).
+        $builder = new ConstraintViolationBuilderStub();
 
         $context = $this->createStub(ExecutionContextInterface::class);
         $context->method('buildViolation')->willReturnCallback(static function (string $message) use (&$messages, $builder): ConstraintViolationBuilderInterface {