sphinx autodoc is failing with launch and launch_ros

[rkent]

both launch and launch_ros packages generate no use useful API documentation. In the launch_ros case, the error is in typing.

See also ros2/launch_ros#232

Typical error:

WARNING: autodoc: failed to import module 'launch_ros'; the following exception was raised:
Traceback (most recent call last):
  File "/workspace/venv/lib/python3.10/site-packages/sphinx/ext/autodoc/importer.py", line 143, in import_module
    return importlib.import_module(modname)
  File "/usr/lib/python3.10/importlib/__init__.py", line 126, in import_module
    return _bootstrap._gcd_import(name[level:], package, level)
  File "<frozen importlib._bootstrap>", line 1050, in _gcd_import
  File "<frozen importlib._bootstrap>", line 1027, in _find_and_load
  File "<frozen importlib._bootstrap>", line 1006, in _find_and_load_unlocked
  File "<frozen importlib._bootstrap>", line 688, in _load_unlocked
  File "<frozen importlib._bootstrap_external>", line 883, in exec_module
  File "<frozen importlib._bootstrap>", line 241, in _call_with_frames_removed
  File "/data2/repos/humble/humble/launch_ros/launch_ros/launch_ros/__init__.py", line 17, in <module>
    from . import actions
  File "/data2/repos/humble/humble/launch_ros/launch_ros/launch_ros/actions/__init__.py", line 17, in <module>
    from .composable_node_container import ComposableNodeContainer
  File "/data2/repos/humble/humble/launch_ros/launch_ros/launch_ros/actions/composable_node_container.py", line 27, in <module>
    from .node import Node
  File "/data2/repos/humble/humble/launch_ros/launch_ros/launch_ros/actions/node.py", line 48, in <module>
    from launch_ros.parameters_type import SomeParameters
  File "/data2/repos/humble/humble/launch_ros/launch_ros/launch_ros/parameters_type.py", line 50, in <module>
    SomeSubstitutionsType_types_tuple +
TypeError: unsupported operand type(s) for +: 'SomeSubstitutionsType_types_tuple' and 'tuple'
 [autodoc.import_object]