[red-knot] Move standalone expr inference to for non-name target (#14788)

## Summary

Ref: https://github.com/astral-sh/ruff/pull/14754#discussion_r1871040646

## Test Plan

Remove the TODO comment and update the mdtest.

crates/red_knot_python_semantic/resources/mdtest/invalid_syntax.md

@@ -26,13 +26,10 @@ def True(for):
     # error: [invalid-syntax]
     pass
 
-# TODO: Why is there two diagnostics for the same error?
-
 # error: [invalid-syntax]
 # error: [invalid-syntax]
 # error: [invalid-syntax]
 # error: [unresolved-reference] "Name `pass` used when not defined"
-# error: [unresolved-reference] "Name `pass` used when not defined"
 for while in pass:
     pass
 
@@ -58,12 +55,10 @@ match while:
 ### Attribute expression
 
 ```py
-# TODO: Why is there two diagnostics for the same error?
 # TODO: Check when support for attribute expressions is added
 
 # error: [invalid-syntax]
 # error: [unresolved-reference] "Name `foo` used when not defined"
-# error: [unresolved-reference] "Name `foo` used when not defined"
 for x in foo.pass:
     pass
 ```