Switch CI from bors to merge queue

[Kobzol]

Context: https://rust-lang.zulipchat.com/#narrow/channel/242791-t-infra/topic/Reducing.20the.20amount.20of.20repos.20that.20use.20bors.2Fhomu

This should be merged with cooperation from an infra-admin.

Opening as a draft, because the CI on this repo is.. interesting :) So I want to make sure that the changes make sense. I renamed clippy_bors.yml to clippy.yml and clippy.yml to clippy_pr.yml, which makes the diff a bit.. tricky.

changelog: Move Clippy from bors to merge queues

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[Kobzol]

Not sure if I understand the CI error: https://github.com/rust-lang/rust-clippy/actions/runs/11513171989/job/32049393605#step:6:39. Does it actually check that the link returns 200? In that case, we'll need to update the badge only after merging this.

[flip1995]

Yes, it checks that all links in our markdown files actually lead to something (this check is actually copied from the Rust repo, so that we don't run into problems during sync).

[Kobzol]

Ok, I removed the badge URL changes, we can fix them up after this is merged.

[Kobzol]

CI failure looks spurious.

[flip1995]

I restarted the run. It was spurious.

[flip1995]

LGTM. We decided to remove the path filters for PRs and run every workflow on every PR: clippy test and clippy dev test ran anyway on almost all PRs and Remark is really quick to run. This way it is possible to require PR CI to be green, before the PR is put into the merge queue. The reviewer still doesn't have to wait for the PR to be green, but can press "merge when ready" before that.