Added Bun packages step

[LeSnake04]

Standards checklist:

• The PR title is descriptive.
• I have read CONTRIBUTING.md
• The code compiles (cargo build)
• The code passes rustfmt (cargo fmt)
• The code passes clippy (cargo clippy)
• The code passes tests (cargo test)
• Optional: I have tested the code myself

For new steps

• Optional: Topgrade skips this step where needed
• Optional: The --dry-run option works with this step
• Optional: The --yes option works with this step if it is supported by
  the underlying command (N/A: no confirmation dialog)

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.

Notes

Bun has a --dry-run command but it lists all installed packages so its output is probably too verbose to be useful for most users.

PS: I triple checked that I didn't forget the require call this time.

[SteveLauC]

Thanks! :)

[JakobFels]

This step fails if there are no packages installed globally (but bun is installed)

bun -g update
No package.json, so nothing to update

[JakobFels]

The step should probably check if
~/.bun/install/global/package.json exists

[LeSnake04]

fixed it #617