[red-knot] have mdformat wrap mdtest files to 100 columns (#14020)

This makes it easier to read and edit (and review changes to) these
files as source, even though it doesn't affect the rendering.

crates/red_knot_python_semantic/resources/mdtest/shadowing/function.md

@@ -2,7 +2,8 @@
 
 ## Parameter
 
-Parameter `x` of type `str` is shadowed and reassigned with a new `int` value inside the function. No diagnostics should be generated.
+Parameter `x` of type `str` is shadowed and reassigned with a new `int` value inside the function.
+No diagnostics should be generated.
 
 ```py path=a.py
 def f(x: str):