make unused_imports less assertive in test modules

[Suyashtnt]

closes #121502

This is a fairly small change and I used the fix suggested in the example expected error message.
Not sure if I should've rather used the alternatives but this one seems the most descriptive.

Some alternatives:

• if this is meant to be a test module, add #[cfg(test)] to the containing module
• try adding #[cfg(test)] to this test module
• consider adding #[allow(unused_imports)] if you want to silent the lint on the unused import
• consider removing the unused import

[rustbot]

Thanks for the pull request, and welcome! The Rust team is excited to review your changes, and you should hear from @michaelwoerister (or someone else) some time within the next two weeks.

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[rustbot]

There are merge commits (commits with multiple parents) in your changes. We have a no merge policy so these commits will need to be removed for this pull request to be merged.

You can start a rebase with the following commands:

$ # rebase
$ git rebase -i master
$ # delete any merge commits in the editor that appears
$ git push --force-with-lease

The following commits are merge commits:

• 361e9b3

[michaelwoerister]

Thanks for the PR, @Suyashtnt! Looks good to me.
@bors r+ rollup

[bors]

📌 Commit 748c615 has been approved by michaelwoerister

It is now in the queue for this repository.