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