fix(coreos-efibootguard.py): fix the script for older python version

On the BIL build container (python v3.8) the script throws an error
which is fixed now.

layers/meta-belden-coreos/lib/devtool/coreos-efibootguard.py

@@ -16,6 +16,7 @@ from devtool import setup_tinfoil, parse_recipe
 from dataclasses import dataclass
 from pathlib import Path
 from shlex import quote
+from typing import List
 
 def register_commands(subparsers, context):
     """Register devtool subcommands from this plugin"""
@@ -125,7 +126,7 @@ class UKIGeneratorArgs:
             f"keydir: {self.keydir}\n"
         )
 
-    def get_buid_cmd(self) -> list[str]:
+    def get_buid_cmd(self) -> List[str]:
         """
         Return the command needed to build the UKI as an array
         """
@@ -141,7 +142,7 @@ class UKIGeneratorArgs:
             args += ["--dtb", dtb]
         return args
 
-    def get_sign_cmd(self) -> list[str]:
+    def get_sign_cmd(self) -> List[str]:
         """
         Return the command needed to sign the UKI in place as an array
         """
@@ -213,7 +214,7 @@ def printi(txt, indent=1, *, iprefix="  ", end="\n"):
     print(textwrap.indent(txt, iprefix * indent), end=end)
 
 
-def dtb_to_list(dtb, deploy_dir) -> list[str]:
+def dtb_to_list(dtb, deploy_dir) -> List[str]:
     """
     Convert the string array from bitbake into a python list. Only the basename
     of the dtb is taken and DEPLOY_DIR is appended