CICD.yml: drop unnecessay setup, simplify

[oech3]

No description provided.

[github-actions]

GNU testsuite comparison:

Skip an intermittent issue tests/date/date-locale-hour (fails in this run but passes in the 'main' branch)
Skip an intermittent issue tests/tail/tail-n0f (fails in this run but passes in the 'main' branch)
Skipping an intermittent issue tests/tail/symlink (passes in this run but fails in the 'main' branch)

[xtqqczze]

The dtolnay/rust-toolchain step only takes a few seconds to run and ensures that we are using the latest stable Rust toolchain and have the required environment variables configured. Is there a particular benefit to removing it?

[oech3]

I prefer reducing num of jobs to reduce risk of network errors and target of audit if we don't need latest stable Rust strictly .