Update CI config and fix CI failure

[taiki-e]

• Update actions/checkout action to v4
• Reduce frequency of scheduled job (daily -> weekly)
  We use stable toolchain in most cases, so we usually don't need to check it every day.
• Remove no longer needed argument for cargo fmt
• Use cargo-hack's --rust-version flag for minrust job
  This respects rust-version field in Cargo.toml, so it removes the need to manage MSRV in both the CI file and Cargo.toml.
• Update ui test output for Rust 1.75
  This fixes CI failure: https://github.com/tokio-rs/async-stream/actions/runs/7428797081/job/20216569930