Address the release of R 4.2

[yutannihilation]

Currently the Windows runner with the r: 'release' is failing: https://github.com/extendr/libR-sys/actions/runs/2209207380 because R 4.2 is released while the setting for r: 'release' is still for R 4.1.

• Slide the CI settings for r: 'release'
• Add an R 4.1 runner for testing Rtools40.
• Remove R 4.2-devel bindings as they won't be needed anymore.

Note that rtools-version specification will not be needed, but it seems it's not the time yet (c.f. r-lib/actions#553)

[yutannihilation]

The bindings for R 4.2 will be generated after merging this, hopefully...

[yutannihilation]

It errors because currently oldrel and release both point to R 4.1 on Ubuntu. I'll retry later...

generated_binding-macOS-latest-R-devel-rust-stable/bindings-macos-x86_64-R4.3-devel.rs
generated_binding-macOS-latest-R-oldrel-rust-stable/bindings-macos-x86_64-R4.1.rs
generated_binding-macOS-latest-R-release-rust-stable/bindings-macos-aarch64-R4.2.rs
generated_binding-macOS-latest-R-release-rust-stable/bindings-macos-x86_64-R4.2.rs
generated_binding-ubuntu-20.04-R-devel-rust-stable/bindings-linux-x86_64-R4.3-devel.rs
generated_binding-ubuntu-20.04-R-oldrel-rust-stable/bindings-linux-x86_64-R4.1.rs
generated_binding-ubuntu-20.04-R-release-rust-stable/bindings-linux-x86_64-R4.1.rs
generated_binding-windows-latest-R-devel-rust-stable-gnu/bindings-windows-x86_64-R4.3-devel.rs
generated_binding-windows-latest-R-oldrel-rust-stable-msvc/bindings-windows-x86-R4.1.rs
generated_binding-windows-latest-R-oldrel-rust-stable-msvc/bindings-windows-x86_64-R4.1.rs
generated_binding-windows-latest-R-release-rust-stable-gnu/bindings-windows-x86_64-R4.2.rs