CI: bump actions/checkout from 4 to 5 for rust-analysis job

CI: bump actions/checkout from 4 to 5 for rust-analysis job

GitHub Actions started complaining about use of Node.js 20 and I was
wondering why only one job uses actions/checkout@v4, while everybody
else already uses actions/checkout@v5.

It turns out that it is caused by a semantic mismerge between
e75cd059 (ci: check formatting of our Rust code, 2025-10-15) that
added a new use of actions/checkout@v4 that happened very close to
another change 63541ed9 (build(deps): bump actions/checkout from 4
to 5, 2025-10-16) that updated all uses of actions/checkout@v4 to
use vactions/checkout@v5.

Update the leftover and the last use of actions/checkout@v4 to use
actions/checkout@v5 to help ourselves to move away from Node.js 20.

Signed-off-by: Junio C Hamano <gitster@pobox.com>