update rust-toolchain to 1.75

[m-tmatma]

rust-toolchain 1.59 prevents the installation of mdbook.

error message

$ cargo install mdbook --vers  0.4.25 --force
    Updating crates.io index
  Installing mdbook v0.4.25
error: failed to compile `mdbook v0.4.25`, intermediate artifacts can be found at `/tmp/cargo-install0wq8YU`

Caused by:
  failed to select a version for the requirement `clap = "^4.0.29"`
  candidate versions found which didn't match: 3.2.25, 3.2.24, 3.2.23, ...
  location searched: crates.io index
  required by package `mdbook v0.4.25`

Link

See rust-lang/mdBook#2269 also