Remove exception message check

Author: cicnavi

tests/src/ValueAbstracts/KeyPairFilenameConfigTest.php

@@ -141,7 +141,6 @@ public function testGetPrivateKeyStringThrowsExceptionWhenFileCannotBeRead(): vo
 
         try {
             $this->expectException(RuntimeException::class);
-            $this->expectExceptionMessage('file');
             $config->getPrivateKeyString();
         } finally {
             chmod($unreadableFile, 0666);