[docs] fix two typos in benchmarks & structs section

docs/source/benchmarks.rst

@@ -72,7 +72,7 @@ The libraries we're comparing are the following:
 - cattrs_ (23.2.3)
 
 Each benchmark creates a message containing one or more ``File``/``Directory``
-instances, then then serializes, deserializes, and validates it in a loop.
+instances, then serializes, deserializes, and validates it in a loop.
 
 The full benchmark source can be found
 `here <https://github.com/jcrist/msgspec/tree/main/benchmarks/bench_validation>`__.

docs/source/structs.rst

@@ -277,7 +277,7 @@ The generated ``__init__()`` for ``Subclass`` looks like:
 
 .. code-block:: python
 
-    def __init__(self, c: float, d: bytes = b"", * a: str, b: int = 0):
+    def __init__(self, c: float, d: bytes = b"", *, a: str, b: int = 0):
 
 The field ordering rules for ``Struct`` types are identical to those for
 `dataclasses`, see the `dataclasses docs <dataclasses>`_ for more information.