test: fix namespace assertion

Signed-off-by: Mark Sagi-Kazar <mark.sagikazar@gmail.com>

Author: sagikazarmark

tests/namespace/test.php

@@ -42,3 +42,4 @@ final public static function exit(): void
 Assert::classExists(\Twirp\Tests\Namespace\Proto\HaberdasherAbstractClient::class);
 Assert::classExists(\Twirp\Tests\Namespace\Proto\HaberdasherJsonClient::class);
 Assert::interfaceExists(\Twirp\Tests\Namespace\Proto\Haberdasher::class);
+Assert::exit();