Fix for rtools_path() failing on R for Windows on ARM (R AARCH64) - 3 filepaths accidentally missing a second backslash

[remlapmot]

I noticed on the new GitHub windows-11-arm runner that devtools::check() fails because of what I think is this simple little bug in pkgbuild::rtools_path() - three filepaths are accidentally missing a second backslash.

Without the fix, the error message one sees is:

Error in get(name, envir = cache) : object 'rtools_path' not found
Calls: <Anonymous> -> cache_get -> get
Execution halted

Here you can see a GitHub Actions run with the error:

https://github.com/remlapmot/pkgbuild-test/actions/runs/14597607865/job/40947417646#step:2:4999

Here you can see a GitHub Actions runs complete successfully with this small fix:

https://github.com/remlapmot/pkgbuild-test/actions/runs/14597791955/job/40948043436#step:2:5024

https://github.com/remlapmot/pkgbuild-test/actions/runs/14598013275/job/40948802415#step:2:7900

[gaborcsardi]

Thank you!