Check that #[deny(allow_attributes)] do not issue spurious messages

[samueltardieu]

Add a new test for #13380. This bug was caused by a bug in rustc which has been fixed in rust-lang/rust@6ee87ae.

Close #13380

changelog: [allow_attributes]: fix spurious warning messages

[rustbot]

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[samueltardieu]

This PR will stay in draft stage until Clippy is synchronized with the latest compiler sources. It will fail until then.

[samueltardieu]

@xFrednet The test is now ready to be added, the rustc merge has happened and the bug is fixed.

[xFrednet]

Thank you for the added test ❤️

---

Roses are #[deny]
Violets are #[allow]
red was triggering,
and an invisible blue

My brain is drained, this is the best poem, I could come up with ^^

[bors]

📌 Commit cc2f447 has been approved by xFrednet

It is now in the queue for this repository.

[bors]

⌛ Testing commit cc2f447 with merge b39323b...

[bors]

☀️ Test successful - checks-action_dev_test, checks-action_remark_test, checks-action_test
Approved by: xFrednet
Pushing b39323b to master...