Move semicolon_if_nothing_returned lint to pedantic

[mbartlett21]

This moves the semicolon_if_nothing_returned lint to pedantic category.

changelog: Move [semicolon_if_nothing_returned] lint into pedantic category.

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[flip1995]

What's the motivation in moving this to style?

[mbartlett21]

According to the formatting guide, this lint is enforcing the preferred style, so I think it should be in that category, rather than restriction.

Use a semi-colon where an expression has void type, even if it could be propagated. E.g.,

fn foo() { ... }

fn bar() {
    foo();
}

https://github.com/rust-dev-tools/fmt-rfcs/blob/master/guide/statements.md

[flip1995]

Since the rust style guidelines recommend that, I guess we could move it to style. But at the same time I feel like this is really pedantic for a warn-by-default lint. So if we move this, we should only move it to pedantic. I'm open for different opinions though.

[camsteffen]

That style guide is in fmt-rfcs which seems to be in a sort of limbo-state, not really an accepted official style guide. Also those guidelines are mainly intended for rustfmt - rules that can be automatically enforced by a formatter. This is a bit of a unique rule since it is "type-aware" which is why Clippy adopted it. So the weird RFC status combined with the "pickiness" makes it fit into pedantic IMO.

Would this be a good time to consider a rename or is it too late? The current name reads badly as allow(semicolon_if_nothing_returned). I'd suggest unit_statements_without_semicolon.

[giraffate]

ping from triage @mbartlett21. Is there anything you still want to discuss?

[mbartlett21]

@giraffate
Thinking over this again, I've now moved this instead to pedantic.

[bors]

☔ The latest upstream changes (presumably #7253) made this pull request unmergeable. Please resolve the merge conflicts.

[mbartlett21]

Now I realise that I should probably not be doing this on my master branch, since I can't rebase very well. I will redo in another branch and make another pr and link it.

EDIT: See #7268