Fix typo in exhaustive_items.rs

[JMoogs]

changelog: none

[rustbot]

Thanks for the pull request, and welcome! The Rust team is excited to review your changes, and you should hear from @y21 (or someone else) some time within the next two weeks.

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[y21]

Thanks!

@bors r+

[bors]

📌 Commit 2d499d8 has been approved by y21

It is now in the queue for this repository.

[bors]

⌛ Testing commit 2d499d8 with merge 4a8c949...

[bors]

☀️ Test successful - checks-action_dev_test, checks-action_remark_test, checks-action_test
Approved by: y21
Pushing 4a8c949 to master...