PR Builds for macOS aarch64 failing due to xcode-select directory

[wcarss]

Problem
Builds for macOS aarch64 are failing during the aarch64-specific items step, reporting the error xcode-select: error: invalid developer directory '/Applications/Xcode_12.2.app/Contents/Developer/'.

Steps

1. Open a PR with cosmetic changes (e.g. Fix grammar in preinstall message. #2874)
2. It fails in the way described.

Possible Solution(s)
My guess is that the latest version of xcode may have changed, and the specified dir doesn't exist anymore. Googling the error brings up stackoverflows of other people experiencing similar issues and suggestions to set the directory to /Library/Developer/CommandLineTools.

Notes

rustup version and show not relevant for this issue

[wcarss]

I'll try putting up a PR with the directory I suggested.

Actually, going to try just removing the whole xcode-select line, since we might not need to specify using a beta compiler at all anymore. @shepmaster as the original author would likely have way better context!

[shepmaster]

we might not need to specify using a beta compiler at all anymore

seems plausible to me!