ty_python_semantic: update "no matching overload" diagnostic test

It looks like support for `@overload` has been added since this test was
created, so we remove the TODO and add a snippet (from #274).

crates/ty_python_semantic/resources/mdtest/diagnostics/no_matching_overload.md

@@ -4,11 +4,15 @@
 
 ## Calls to overloaded functions
 
-TODO: Note that we do not yet support the `@overload` decorator to define overloaded functions in
-real Python code. We are instead testing a special-cased function where we create an overloaded
-signature internally. Update this to an `@overload` function in the Python snippet itself once we
-can.
-
 ```py
-type("Foo", ())  # error: [no-matching-overload]
+from typing import overload
+
+@overload
+def f(x: int) -> int: ...
+@overload
+def f(x: str) -> str: ...
+def f(x: int | str) -> int | str:
+    return x
+
+f(b"foo")  # error: [no-matching-overload]
 ```