bpo-41681 Fixed mistake in test for f-string/str.format error description (GH-22036)

[millefalcon]

@ericvsmith Fixed mistake in two of the error description test for f-string/str.format.

def test_with_an_underscore_and_a_comma_in_format_specifier(self):
    error_msg = re.escape("Cannot specify both ',' and '_'.")
    with self.assertRaisesRegex(ValueError, error_msg):
        '{:,_}'.format(1)

Should have been,

def test_with_an_underscore_and_a_comma_in_format_specifier(self):
    error_msg = re.escape("Cannot specify both ',' and '_'.")
    with self.assertRaisesRegex(ValueError, error_msg):
        '{:_,}'.format(1)

And

def test_with_an_underscore_and_a_comma_in_format_specifier(self):
    error_msg = re.escape("Cannot specify both ',' and '_'.")
    with self.assertRaisesRegex(ValueError, error_msg):
        f'{1:,_}'

Should have been,

def test_with_an_underscore_and_a_comma_in_format_specifier(self):
    error_msg = re.escape("Cannot specify both ',' and '_'.")
    with self.assertRaisesRegex(ValueError, error_msg):
        f'{1:_,}'

https://bugs.python.org/issue41681

[miss-islington]

Thanks @millefalcon for the PR, and @ericvsmith for merging it 🌮🎉.. I'm working now to backport this PR to: 3.9.
🐍🍒⛏🤖

[bedevere-bot]

GH-22060 is a backport of this pull request to the 3.9 branch.