Run cleanup after each integration test

This is needed to get rid of posts created in tests to prevent test interdependency
[MAILPOET-6335]

packages/php/email-editor/tests/integration/_bootstrap.php

@@ -105,6 +105,14 @@ abstract class MailPoetTest extends \Codeception\TestCase\Test { // phpcs:ignore
 		parent::setUp();
 	}
 
+	/**
+	 * Tear down after each test.
+	 */
+	public function _after() {
+		parent::_after();
+		$this->tester->cleanup();
+	}
+
 	/**
 	 * Check if the HTML is valid.
 	 *