Add purplesyringa to cloud-compute

[purplesyringa]

I wanted to work on some LLVM features to improve unwinding support on Windows but don't really have enough compute to play around with LLVM. @ChrisDenton told me I could ask for a dev desktop here.

[github-actions]

Dry-run check results

[WARN  sync_team] sync-team is running in dry mode, no changes will be applied.
[INFO  sync_team] synchronizing github
[INFO  sync_team] 💻 Team Diffs:
    📝 Editing team 'rust-lang/cloud-compute-team':
      Adding member 'purplesyringa' with member role

[ChrisDenton]

I'd love for purplesyringa to have access to the dev desktops to help investigate and improve our unwinding support!