Fix building for Android, enable `tlmgr` updates

[MrAdityaAlok]

• fix(os/unix): cannot find SkipStep while building for android
• feat: enable tlmgr updates for android

Standards checklist:

• [x] The PR title is descriptive.
• [x] The code compiles (cargo build)
• [x] The code passes rustfmt (cargo fmt)
• [x] The code passes clippy (cargo clippy)
• [x] The code passes tests (cargo test)
• [x] Optional: I have tested the code myself
  • [x] I also tested that Topgrade skips the step where needed

If you developed a feature or a bug fix for someone else and you do not have the means to test it, please tag this person here.

Closes #895