Convert phrase to string

(cherry picked from commit 3dbfc5e)

Author: schmengler

dev/tests/integration/framework/tests/unit/testsuite/Magento/Test/Bootstrap/SettingsTest.php

@@ -200,7 +200,7 @@ public function getAsConfigFileDataProvider()
     public function testGetAsConfigFileException($settingName, $expectedExceptionMsg)
     {
         $this->expectException(\Magento\Framework\Exception\LocalizedException::class);
-        $this->expectExceptionMessage($expectedExceptionMsg);
+        $this->expectExceptionMessage((string)$expectedExceptionMsg);
         $this->_object->getAsConfigFile($settingName);
     }