Add test case for issue#6082

[shulaoda]

Related to #6099, #6082

If you want, you can also add the code snippet from #6082 (comment) as a separate test case, which deals with the same issue and contains a complete code snippet without any parse errors. No problem if not. If you choose to also include that code snippet all you'd need to do is add it to a file in the tests/target directory, which is typically what you'd do when adding test cases to rustfmt.

Originally posted by @ytmimi in #6099

[jieyouxu]

As far as I can tell, #6099 can be considered fully resolved, because this fixed on the r-l/r side in rust-lang/rust#121487

rustfmt/src/test/parser.rs

Line 62 in acf51c8

let filename = "tests/parser/stashed-diag.rs";

rustfmt/tests/parser/stashed-diag.rs

Lines 1 to 3 in acf51c8

	#![u={static N;}]
	fn main() {}

so IMO this test is redundant, since it's due to the same root cause where rustfmt uses rustc's parser but not through run_compiler, and so needs to handle stashed diagnostics explicitly.

Thanks regardless though!