fix(typing): User may not have provided a return annotation for an overload

[bzoracler]

If the source code doesn't provide a return type annotation on one or more overloads, then 1-indexed value of the inner tuple, representing the annotation, can be None.

This is a consequence of the following:

sphinx-autoapi/autoapi/_parser.py

Lines 459 to 461 in 6dae5a3

	grouped["overloads"].append(
	(child_data["args"], child_data["return_annotation"])
	)

sphinx-autoapi/autoapi/_parser.py

Line 303 in 6dae5a3

"return_annotation": _astroid_utils.get_return_annotation(node),

sphinx-autoapi/autoapi/_astroid_utils.py

Line 665 in 6dae5a3

def get_return_annotation(node: astroid.nodes.FunctionDef) -> str | None: