CI: Enable RUST_BACKTRACE for tests

[n0toose]

Could be useful in some cases when GitHub Actions fails on a specific target.

[n0toose]

I went through with issuing a PR for this because I think I missed it in: #701 (comment)

Having the backtrace in the logs in the first place would be optimal - provided that I don't make an identical commit in my own tree just to be able to read the backtrace and then undo it - or by using a system that I can SSH onto.

(Note: This was a quick change and I did not test it against the sysinfo PR or otherwise)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 68.17%. Comparing base (e9fc8de) to head (e8340ed).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #723   +/-   ##
=======================================
  Coverage   68.17%   68.17%           
=======================================
  Files          20       20           
  Lines        2319     2319           
=======================================
  Hits         1581     1581           
  Misses        738      738           

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[n0toose]

Replaced full with 1, because that's what the Rust toolchain instructs you to do - I imagined it might be more direct than full.

It's also what rust-lang/rust does: https://github.com/rust-lang/rust/actions/runs/5192558478/workflow