[pep-0591] clarify that type checkers may not allow `Final` in loops (#1033)

pep-0591.rst

@@ -175,8 +175,9 @@ names in type-checked code::
    RATE = 300  # Error: can't assign to final attribute
    Base.DEFAULT_ID = 1  # Error: can't override a final attribute
 
-   for x in [1, 2, 3]:
-      FOO: Final = x  # Error: Cannot use Final inside a loop
+Note that a type checker need not allow ``Final`` declarations inside loops
+since the runtime will see multiple assignments to the same variable in
+subsequent iterations.
 
 Additionally, a type checker should prevent final attributes from
 being overridden in a subclass::