stubtest crash when a referenced module is a DLL #13822

PS C:\Users\Avasam\Documents\Git\typeshed> python .\tests\stubtest_third_party.py pywin32
pywin32... fail

C:\Users\Avasam\AppData\Local\Temp\tmp3yxfa81_\Scripts\pip.exe install pywin32[]==304.* mypy==0.982
MYPYPATH=C:\Users\Avasam\Documents\Git\typeshed\stubs\pywin32 C:\Users\Avasam\AppData\Local\Temp\tmp3yxfa81_\Scripts\python.exe -m mypy.stubtest --custom-typeshed-dir C:\Users\Avasam\Documents\Git\typeshed pythonwin win32 win32comext pythoncom _win32typing --allowlist C:\Users\Avasam\Documents\Git\typeshed\stubs\pywin32\@tests\stubtest_allowlist.txt

Traceback (most recent call last):
  File "C:\Program Files\Python39\lib\tokenize.py", line 330, in find_cookie
    line_string = line.decode('utf-8')
UnicodeDecodeError: 'utf-8' codec can't decode byte 0x90 in position 2: invalid start byte

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "C:\Program Files\Python39\lib\runpy.py", line 197, in _run_module_as_main
    return _run_code(code, main_globals, None,
  File "C:\Program Files\Python39\lib\runpy.py", line 87, in _run_code
    exec(code, run_globals)
  File "C:\Users\Avasam\AppData\Local\Temp\tmp3yxfa81_\lib\site-packages\mypy\stubtest.py", line 1713, in <module>
    sys.exit(main())
  File "C:\Users\Avasam\AppData\Local\Temp\tmp3yxfa81_\lib\site-packages\mypy\stubtest.py", line 1709, in main
    return test_stubs(parse_options(sys.argv[1:]))
  File "C:\Users\Avasam\AppData\Local\Temp\tmp3yxfa81_\lib\site-packages\mypy\stubtest.py", line 1605, in test_stubs
    print(error.get_description(concise=args.concise))
  File "C:\Users\Avasam\AppData\Local\Temp\tmp3yxfa81_\lib\site-packages\mypy\stubtest.py", line 138, in get_description
    runtime_line = inspect.getsourcelines(self.runtime_object)[1]
  File "C:\Program Files\Python39\lib\inspect.py", line 1006, in getsourcelines
    lines, lnum = findsource(object)
  File "C:\Program Files\Python39\lib\inspect.py", line 831, in findsource
    lines = linecache.getlines(file, module.__dict__)
  File "C:\Program Files\Python39\lib\linecache.py", line 46, in getlines
    return updatecache(filename, module_globals)
  File "C:\Program Files\Python39\lib\linecache.py", line 136, in updatecache
    with tokenize.open(fullname) as fp:
  File "C:\Program Files\Python39\lib\tokenize.py", line 394, in open
    encoding, lines = detect_encoding(buffer.readline)
  File "C:\Program Files\Python39\lib\tokenize.py", line 371, in detect_encoding
    encoding = find_cookie(first)
  File "C:\Program Files\Python39\lib\tokenize.py", line 335, in find_cookie
    raise SyntaxError(msg)
SyntaxError: invalid or missing encoding declaration for 'C:\\Users\\Avasam\\AppData\\Local\\Temp\\tmp3yxfa81_\\lib\\site-packages\\pywin32_system32\\pywintypes39.dll'