Update touchstone GHA to use touchstone@main

[VisruthSK]

Change touchstone GHA to download latest version of touchstone package instead of v1. This should fix this empty comment which is due to the branch having a slash.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 92.70%. Comparing base (286263d) to head (2bc6536).
⚠️ Report is 2 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #372   +/-   ##
=======================================
  Coverage   92.70%   92.70%           
=======================================
  Files          31       31           
  Lines        3029     3029           
=======================================
  Hits         2808     2808           
  Misses        221      221           

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[github-actions]

This is how benchmark results would change (along with a 95% confidence interval in relative change) if 2bc6536 is merged into master:

• ✔️loo_function: 1.92s -> 1.93s [-0.05%, +0.5%]
• ❗🐌loo_matrix: 1.7s -> 1.71s [+0.67%, +1.46%]
  Further explanation regarding interpretation and methodology can be found in the documentation.