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

## Summary

Ref: #14754 (comment)

## Test Plan

Remove the TODO comment and update the mdtest.

Author: dhruvmanila

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
 ```

crates/red_knot_python_semantic/src/types/infer.rs

@@ -1900,12 +1900,11 @@ impl<'db> TypeInferenceBuilder<'db> {
             is_async: _,
         } = for_statement;
 
-        self.infer_standalone_expression(iter);
-
         // TODO more complex assignment targets
         if let ast::Expr::Name(name) = &**target {
             self.infer_definition(name);
         } else {
+            self.infer_standalone_expression(iter);
             self.infer_expression(target);
         }
         self.infer_body(body);