Remove redundant assertIsArray after return type narrowing

The buildCommandArray return type is now always array (no longer
array|string), so phpstan correctly flags the assertion as tautological.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: aarondfrancis

tests/Unit/ManagesProcessTest.php

@@ -30,7 +30,6 @@ public function buildWithDimensions(): array
 
         $result = $command->buildWithDimensions();
 
-        $this->assertIsArray($result['built']);
         $this->assertSame('bash', $result['built'][0]);
         $this->assertSame('-lc', $result['built'][1]);
         $this->assertStringContainsString(