Allow to use Literal for all python versions

kiwi/bootloader/config/__init__.py

@@ -15,7 +15,13 @@
 # You should have received a copy of the GNU General Public License
 # along with kiwi.  If not, see <http://www.gnu.org/licenses/>
 #
-from typing import TYPE_CHECKING, Dict, Literal, Union, overload
+import sys
+from typing import TYPE_CHECKING, Dict, Union, overload
+
+if sys.version_info >= (3, 8):
+    from typing import Literal  # pragma: no cover
+else:  # pragma: no cover
+    from typing_extensions import Literal  # pragma: no cover
 
 from kiwi.exceptions import (
     KiwiBootLoaderConfigSetupError