Fix FP in wrong_self_convention lint

[ThibsG]

Previously, this lint didn't check into impl block when it was implementing a trait.
Recent improvements (#6924) have moved this check and some impl blocks are now checked but they shouldn't, such as in #7032.

Fixes #7032

changelog: Fix FP when not taking self in impl block for [wrong_self_convention] lint

[rust-highfive]

r? @giraffate

(rust-highfive has picked a reviewer for you, use r? to override)

[giraffate]

It looks good, thanks!

@ThibsG Can you update changelog? This fixes FP, so I don't think changelog: none is appropriate.

[ThibsG]

Yes of course, I was get used to let the reviewer set the appropriate text for changelog (mostly to keep coherence I think) 😄

[giraffate]

@bors r+

Thanks!

[bors]

📌 Commit 3ce6f0d has been approved by giraffate

[bors]

⌛ Testing commit 3ce6f0d with merge 411c0df...

[flip1995]

@giraffate as a team member you should now be able to change the PR body description on your own, so that you don't have to wait on the author.

[flip1995]

@ThibsG There is no real syntax for this line. The only thing that helps (me) when writing the changelog is when the lint name is put into brackets [] AND backticks ` `, so [`lint_name`].

[giraffate]

Oh, thanks for teaching me that!

[bors]

☀️ Test successful - checks-action_dev_test, checks-action_remark_test, checks-action_test
Approved by: giraffate
Pushing 411c0df to master...