glasgow build also has importlib issues with python <3.10

[txf-]

Using Python 3.9. I updated to the latest version and glasgow --version executes correctly:

PS C:\Users\Tiago\Documents\Git> glasgow.exe --version
Glasgow version 0.1.dev1827+g613cdc1 (Python 3.9.0)

I assume this is related to #408

PS C:\Users\Tiago\Documents\Git> glasgow build --rev C3 uart
Traceback (most recent call last):
  File "C:\Users\Tiago\.local\pipx\venvs\glasgow\lib\site-packages\importlib_metadata\__init__.py", line 292, in __getitem__
    return next(iter(self.select(name=name)))
StopIteration

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "c:\python39\lib\runpy.py", line 197, in _run_module_as_main
    return _run_code(code, main_globals, None,
  File "c:\python39\lib\runpy.py", line 87, in _run_code
    exec(code, run_globals)
  File "c:\users\tiago\.local\bin\glasgow.exe\__main__.py", line 7, in <module>
  File "C:\Users\Tiago\Documents\Git\glasgow\software\glasgow\cli.py", line 910, in main
    exit(loop.run_until_complete(_main()))
  File "c:\python39\lib\asyncio\base_events.py", line 642, in run_until_complete
    return future.result()
  File "C:\Users\Tiago\Documents\Git\glasgow\software\glasgow\cli.py", line 794, in _main
    target, applet = _applet(args.rev, args)
  File "C:\Users\Tiago\Documents\Git\glasgow\software\glasgow\cli.py", line 398, in _applet
    applet = GlasgowAppletMetadata.get(args.applet).applet_cls()
  File "C:\Users\Tiago\Documents\Git\glasgow\software\glasgow\support\plugin.py", line 70, in get
    return cls(importlib_metadata.entry_points(group=cls.GROUP_NAME, name=handle)[0])
  File "C:\Users\Tiago\.local\pipx\venvs\glasgow\lib\site-packages\importlib_metadata\__init__.py", line 294, in __getitem__
    raise KeyError(name)
KeyError: 0