[ty] Add mdtest suite for typing.Concatenate (#23554)

## Summary

This PR adds a comprehensive test suite for `typing.Concatenate` in
preparation for astral-sh/ty#1535 and to help
the review process in #23119.

## Test Plan

Run mdtest.

Author: dhruvmanila

crates/ty_python_semantic/resources/mdtest/annotations/callable.md

@@ -373,14 +373,6 @@ def _(c: Callable[Concatenate[int, str, ...], int]):
     reveal_type(c)  # revealed: (...) -> int
 ```
 
-And, as one of the parameter types:
-
-```py
-def _(c: Callable[[Concatenate[int, str, ...], int], int]):
-    # TODO: Should reveal the correct signature
-    reveal_type(c)  # revealed: (...) -> int
-```
-
 Other type expressions can be nested inside `Concatenate`:
 
 ```py