Add test for bug-12253 with additionalConstructors configured

Adds a PayloadWithAdditionalConstructor test class that reproduces the
same readonly property false positive scenario but with setUp() configured
as an additional constructor via ConstructorsHelper.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: phpstan-bot

tests/PHPStan/Rules/Properties/MissingReadOnlyPropertyAssignRuleTest.php

@@ -26,6 +26,7 @@ protected function getRule(): Rule
 					'Bug10523\\Controller::init',
 					'Bug10523\\MultipleWrites::init',
 					'Bug10523\\SingleWriteInConstructorCalledMethod::init',
+					'Bug12253\\PayloadWithAdditionalConstructor::setUp',
 				],
 			),
 		);

tests/PHPStan/Rules/Properties/data/bug-12253.php

@@ -46,6 +46,50 @@ private function validationValue(mixed $value): mixed
 	}
 }
 
+class PayloadWithAdditionalConstructor
+{
+	/** @var array<array<string, mixed>> */
+	private(set) readonly array $validation;
+
+	/** @var array<string, string> */
+	private array $ids = [];
+
+	public function __construct(private readonly stdClass $payload)
+	{
+	}
+
+	public function setUp(): void
+	{
+		$this->parseValidation();
+	}
+
+	private function parseValidation(): void
+	{
+		$validations = [];
+
+		foreach ($this->payload->validation as $key => $validation) {
+			$validations[] = [
+				'id' => $key,
+				'field_id' => $this->ids[$validation->field_id],
+				'rule' => $validation->rule,
+				'value' => $this->validationValue($validation->value),
+				'message' => $validation->message,
+			];
+		}
+
+		$this->validation = $validations;
+	}
+
+	private function validationValue(mixed $value): mixed
+	{
+		if (is_null($value)) {
+			return null;
+		}
+
+		return $this->ids[$value] ?? $value;
+	}
+}
+
 class PayloadWithoutAsymmetricVisibility
 {
 	/** @var array<array<string, mixed>> */