docs: fix typo in prev_siblings_are docstring (#5281)

Author: TheGreatApollyon

src/black/nodes.py

@@ -457,7 +457,7 @@ def preceding_leaf(node: LN | None) -> Leaf | None:
 
 def prev_siblings_are(node: LN | None, tokens: list[NodeType | None]) -> bool:
     """Return if the `node` and its previous siblings match types against the provided
-    list of tokens; the provided `node`has its type matched against the last element in
+    list of tokens; the provided `node` has its type matched against the last element in
     the list.  `None` can be used as the first element to declare that the start of the
     list is anchored at the start of its parent's children."""
     if not tokens: