[3.12] DOCS: Suggest always calling exec with a globals argument and no locals argument (GH-119235)

[miss-islington]

Many users think they want a locals argument for various reasons but they do not
understand that it makes code be treated as a class definition. They do not want
their code treated as a class definition and get surprised. The reason not
to pass locals specifically is that the following code raises a NameError:

exec("""
def f():
    print("hi")

f()

def g():
    f()
g()
""", {}, {})

The reason not to leave out globals is as follows:

def t():
    exec("""
def f():
    print("hi")

f()

def g():
    f()
g()
    """)

(cherry picked from commit 7e1a130)

Co-authored-by: Hood Chatham roberthoodchatham@gmail.com

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