test(pool): propagate the schema mode across two borrows without counting on setSchemaless() to borrow

Pool::setSchemaless() no longer checks a connection out, so the test now
borrows twice after setting the mode and checks both connections are in
it.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

Author: abnegate

tests/unit/Adapter/PoolTest.php

@@ -172,6 +172,8 @@ static function (callable $callback) use (&$adapters): mixed {
         $pool->setSchemaless(true);
 
         $this->assertFalse($pool->supports(Capability::DefinedAttributes));
+        $this->assertTrue($pool->isSchemaless());
+        $this->assertFalse($first->supports(Capability::DefinedAttributes));
         $this->assertFalse($second->supports(Capability::DefinedAttributes));
     }