fix(ghcache.py): emit files to upload in data/tmp

[bassosimone]

This provides for a slightly better DX.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.17%. Comparing base (1d6efc4) to head (f86d353).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #127   +/-   ##
=======================================
  Coverage   99.17%   99.17%           
=======================================
  Files          37       37           
  Lines        2295     2295           
=======================================
  Hits         2276     2276           
  Misses         19       19           

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

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.