1.28.0 release planning

[djc]

As discussed in #3985 (comment), starting an issue for this because it makes it easier to have a discussion in one place on what items should be in the milestone(s).

I would propose that we remove these from the 1.28.0 milestone:

• rustup-init leaves user with colored terminal #2590
• rustup self uninstall fails on Windows if a custom toolchain is installed #2789
• rustup set default-host does not change the default toolchain #3651

Tasks

• Prepare 1.28.0 release #4079
• Prepare 1.28.0: step 2 #4098
• ci(stable): fix build issues to prepare for v1.28.0 release #4105

[rami3l]

Remaining concerns for the beta release:

• Related CI errors (https://github.com/rust-lang/rustup/actions/runs/12153440399)
• Add loongarch64-unknown-linux-musl support #3921 (comment)

The beta release is now available in https://internals.rust-lang.org/t/seeking-beta-testers-for-rustup-v1-28-0.

Remaining concerns for the stable release:

• rustup default no longer exits with 1 with no default toolchain is set #4140