wix packages: fix annotations for old python

Current cerbero-uninstalled script limits the python version by:

    if not sys.version_info >= (3, 7, 0):

But on 3.8.10 (used in Ubuntu 20.04.6 LTS Focal Fossa) we've got:

# ./cerbero-uninstalled --help
WARNING: Running as root
Traceback (most recent call last):
  File "<string>", line 24, in <module>
  File "/root/github/cerbero/cerbero/main.py", line 224, in main
    Main(sys.argv[1:])
  File "/root/github/cerbero/cerbero/main.py", line 46, in __init__
    self.load_commands()
  File "/root/github/cerbero/cerbero/main.py", line 164, in load_commands
    commands.load_commands(subparsers)
  File "/root/github/cerbero/cerbero/commands/__init__.py", line 67, in load_commands
    __import__('cerbero.commands.%s' % name)
  File "/root/github/cerbero/cerbero/commands/package.py", line 26, in <module>
    from cerbero.packages.packager import Packager
  File "/root/github/cerbero/cerbero/packages/packager.py", line 72, in <module>
    from cerbero.packages.windows import wix_on_ninja  # noqa: E402
  File "/root/github/cerbero/cerbero/packages/windows/wix_on_ninja.py", line 19, in <module>
    class Candle(object):
  File "/root/github/cerbero/cerbero/packages/windows/wix_on_ninja.py", line 24, in Candle
    def compile(self, writer: Writer, inputs: list[str], output: str, implicit_outputs=None, implicit_deps=None):
TypeError: 'type' object is not subscriptable