ci: update upload-artifact to 3.1.1 to remove set-output warnings

[ClementTsang]

Description

A description of the change, what it does, and why it was made. If relevant (such as any change that modifies the UI), please provide screenshots of the changes:

This resolves this GitHub Actions deprecation warning by updating the action version.

For more context, see #846.

Issue

If applicable, what issue does this address?

Closes: #

Testing

If relevant, please state how this was tested. All changes must be tested to work:

If this is a code change, please also indicate which platforms were tested:

All affected workflows should pass, though it might be hard to test deployment without some extra work. We'll mainly just test nightly instead, which should be fine as there are no breaking changes. The previous warning should be gone.

The run can be found here: https://github.com/ClementTsang/bottom/actions/runs/3443313490

Checklist

If relevant, ensure the following have been met:

• Areas your change affects have been linted using rustfmt (cargo fmt)
• The change has been tested and doesn't appear to cause any unintended breakage
• Documentation has been added/updated if needed (README.md, help menu, doc pages, etc.)
• The pull request passes the provided CI pipeline
• There are no merge conflicts
• If relevant, new tests were added (don't worry too much about coverage)