BaseTools: Skip directories with code extensions in the name

Currently openssl has an Open Quantum Safe provider submodule with
directories like oqs-provider/oqs-template/oqsprov/oqsprov.c or
oqs-provider/oqs-template/oqsprov/oqsprov/oqsprov_capabilities.c
that are used as templates, but DebugMacroCheck tries to read them
as a file when recursively traversing the subdirectories.

Fail message:

  File "/usr/lib/python3.10/pathlib.py", line 1119, in open
    return self._accessor.open(self, mode, buffering, encoding, errors,
  IsADirectoryError: [Errno 21] Is a directory: '/CryptoPkg/Library
/OpensslLib/openssl/oqs-provider/oqs-template/oqsprov/oqsprov.c'

Signed-off-by: Alexander Gryanko <xpahos@gmail.com>

BaseTools/Plugin/DebugMacroCheck/DebugMacroCheck.py

@@ -429,7 +429,7 @@ def _show_file_discovered_message(file_count: int,
 
         files = []
         for file in root_directory.rglob('*'):
-            if file.suffix in extensions:
+            if file.suffix in extensions and not file.is_dir:
                 files.append(Path(file))
 
             # Give an indicator progress is being made