Multiplier::validate(): Filter out non-validatable components

45ed76a started filtering components
to `Control`s, to appease PHPStan, since `Container::validate()` only
accepts `Control[]`. But `Multiplier` does not actually have `Control`s
as direct children (other than the ‘Add’ `Submitter`s), so it would stop
validating and filtering multiplied controls.

a5a7348 reverted that part but kept
the incorrect phpdoc type cast.

Now, it works without the filter because `Container::validate()` already
ignores non-validatable components but we should still respect its contract.

Let’s filter the components before passing them down. This will also
allow us to drop the lying phpdoc type cast.

src/Multiplier.php

@@ -169,8 +169,8 @@ public function addCreateButton(?string $caption = null, int $copyCount = 1): Cr
 	 */
 	public function validate(?array $controls = null): void
 	{
-		/** @var Control[] $components */
-		$components = $controls ?? $this->getComponents();
+		/** @var (Control|Container)[] $components */
+		$components = $controls ?? array_filter($this->getComponents(), fn ($component) => $component instanceof Control || $component instanceof Container);
 
 		foreach ($components as $index => $control) {
 			foreach ($this->noValidate as $item) {