chore: fix capture

koerce/patterns.py

@@ -1232,7 +1232,7 @@ def __init__(self, key: str | Deferred | Builder, what=_any):
                 key = key.name
             else:
                 raise TypeError("Only variables can be used as capture keys")
-        self.key = key
+        self.key = cython.cast(str, key)
         self.what = pattern(what)
 
     def __repr__(self) -> str: