Add type annotation for __getitem__

Author: domdfcoding

sphinx_pyproject/__init__.py

@@ -175,7 +175,7 @@ def __init__(
 			globalns.update(pep621_config)
 			globalns.update(self._freeform)
 
-	def __getitem__(self, item) -> Any:
+	def __getitem__(self, item: str) -> Any:
 		"""
 		Returns the value of the given key in the  ``tool.sphinx-pyproject`` table.