fix: use the origin type when validating a grammar list (#82)

issubclass working on a GenericAlias was a bug that was fixed in python 3.13 (see python/cpython#101162)

Fixes #81

Signed-off-by: Paul Mars <paul.mars@canonical.com>

Author: upils

craft_grammar/models.py

@@ -74,6 +74,7 @@ def _validate_grammar_list(  # noqa: PLR0912
     ) -> list[T]:
         # Check if the type_ is supposed to be a list
         sub_type: Any = get_args(type_)
+        unsubscripted_type = get_origin(type_) or type_
 
         # handle typed list
         if sub_type:
@@ -121,7 +122,7 @@ def _validate_grammar_list(  # noqa: PLR0912
                     pass
                 else:
                     continue
-            if issubclass(type_, str):
+            if issubclass(unsubscripted_type, str):
                 if isinstance(item, dict):
                     errors.append(
                         pydantic_core.InitErrorDetails(