Pin Rust toolchain

[szokeasaurusrex]

Pin Rust toolchain minor version to prevent new Clippy lints from breaking CI. As a follow-up, let's add a job to auto-open PRs when a new toolchain version is available

[linear]

CLI-152 Pin Rust toolchain

[szokeasaurusrex]

#2692 reverts, so I am reopening the issue