fix literal_string_with_formatting_args FP on format inside assert

[profetia]

fixes: #13885

I found that the error message generated by assert is put on a root context, not sure if it is a bug on the compiler side (I tested dbg and everything went fine, though I do found the generated file name is on a root context too). I simply guarded the lint behind is_dummy.

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changelog: [literal_string_with_formatting_args] fix FP on format inside assert

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[tamird]

I'm not a clippy expert but this fix looks like a hack to me. Why don't we want to report these? The bug I reported is that this FP happens even when I put an #[allow(...)] on the expression.

[profetia]

@tamird I think you misunderstand my point. This FP happens because clippy is linting the panicked message generated by assert!. So adding an #[allow(...)] on the expression will not affected the generated string literal.

fn test_parse() {
    if !parse(#[allow(clippy::literal_string_with_formatting_args)] "foo {:}").is_err()
            {
            ::core::panicking::panic("assertion failed: parse(#[allow(clippy::literal_string_with_formatting_args)] \"foo {:}\").is_err()") // This is line is causing the FP
        };
}

[GuillaumeGomez]

I'm not sure this is the right fix. The problem here was that I was working on dummy spans, which is why the lint seemed to be emitted on completely unrelated code. I opened #13953.