Fix typo in ExitCode (#17294)

A missing letter, nothing more

framework/console/ExitCode.php

@@ -133,7 +133,7 @@ class ExitCode
         self::NOINPUT => 'Input file not found or unreadable',
         self::NOUSER => 'User not found',
         self::NOHOST => 'Host not found',
-        self::UNAVAILABLE => 'A requied service is unavailable',
+        self::UNAVAILABLE => 'A required service is unavailable',
         self::SOFTWARE => 'Internal error',
         self::OSERR => 'Error making system call or using OS service',
         self::OSFILE => 'Error accessing system file',