[misrefactored_assign_op]: Fix duplicate diagnostics

[high-cloud]

Relate to #12379

The following diagnostics appear twice

  --> tests/ui/assign_ops2.rs:26:5
   |
LL |     a *= a * a;
   |     ^^^^^^^^^^
   |
help: did you mean `a = a * a` or `a = a * a * a`? Consider replacing it with

because a (lhs) appears in both left operand and right operand in the right hand side.
This PR fixes the issue so that if a diagnostic is created for an operand, the check of the other operand will be skipped. It's fine because the result is always the same in the affected operators.

changelog: [misrefactored_assign_op]: Fix duplicate diagnostics

[rustbot]

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

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[flip1995]

I love how those duplicated diags get addressed one by one right now! Especially by first time contributors. Thanks and welcome to Clippy!

LGTM, blessing the tests seemed to have gone wrong. Please run cargo bless and squash that into your commit, then this is good to go.

[high-cloud]

Thanks for advice. I have updated assign_ops2.stderr now. @rustbot review

[flip1995]

@bors r+

Thanks!

[bors]

📌 Commit 3c5008e has been approved by flip1995

It is now in the queue for this repository.

[bors]

⌛ Testing commit 3c5008e with merge 2d9d404...

[bors]

☀️ Test successful - checks-action_dev_test, checks-action_remark_test, checks-action_test
Approved by: flip1995
Pushing 2d9d404 to master...