Fix PT014 autofix for last item in list

[augustelalande]

Summary

This error was found browsing https://github.com/qarmin/Automated-Fuzzer/actions/runs/8396966850. Which failed when trying to autofix the PT014 violation in the following code:

@pytest.mark.parametrize('data, spec', [(1.0, 1.0), (1.0, 1.0)])
def test_numbers(data, spec):
    ...

Investigation revealed that the implementation was not properly tested, when the duplicate value was also the last in the list. In particular the following function, which is in charge of finding the comma following an element to create the suggested fix,

ruff/crates/ruff_linter/src/rules/flake8_pytest_style/rules/parametrize.rs

Lines 647 to 651 in 0a99bd8

	fn trailing_comma(element: &Expr, source: &str) -> Option<TextSize> {
	SimpleTokenizer::starts_at(element.end(), source)
	.find(|token| token.kind == SimpleTokenKind::Comma)
	.map(|token| token.start())
	}

would find the next comma even if it was outside the list itself leading to a lot of code being deleted.

This PR fixes that.

Test Plan

Added misbehaving code to the test fixture.

[github-actions]

ruff-ecosystem results

Linter (stable)

✅ ecosystem check detected no linter changes.

Linter (preview)

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Formatter (stable)

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Formatter (preview)

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