"Local variable (defined in enclosing scope) referenced before assignment" wording is misleading

def f():
    x = None
    def g():
        # Programmer forgot to add `nonlocal` here.
        if x is None:
            x = "hello"

foo.py:5:12: F823 local variable 'x' (defined in enclosing scope on line 2) referenced before assignment

But it's not the variable defined on line 2 which is being referenced before assignment, it's the one defined on line 6. The programmer thinks they're using the one on line 2, and the message only reinforces their mistake.

Suggest rephrase to something like (shadowing name from line 2 in enclosing scope).

(There's a similar example in #315 where the enclosing scope was global.)

Start by locating the code that formats the F823 diagnostic, then compare its wording with the example in this issue and the related example in #315. Done means the message clearly describes the inner name as shadowing the enclosing-scope name rather than saying the enclosing variable was referenced before assignment.