Improve pixi global update reporting

[Hofer-Julian]

It should output one of these things:

• Up-to-date
• Updated top-level dependencies to these versions
• Updated environment (when only transitive dependencies have been updated)

Current status:

$ pixi global update
✔ Updated environment rattler-build.

The output would stay the same when only transitive dependencies have been updated.

New output when nothing has been updated:

$ pixi global update
✔ Environment rattler-build was already up-to-date.

Output when a single top-level dependency has been updated

$ pixi global update
✔ Updated package rattler-build in environment rattler-build.

Output when multiple top-level dependencies have been updated

$ pixi global update
✔ Updated packages in environment rattler-build.
    - rattler-build
    - patch-elf
    - grep