Turn cppyy on llvm 20 jobs

[mcbarton]

Description

Please include a summary of changes, motivation and context for this PR.

This PR will turn on cppyy for the llvm 20 jobs. This will require an identical PR in cppyy to create any needed Valgrind suppression files.

Fixes # (issue)

Type of change

Please tick all options which are relevant.

• Bug fix
• New feature
• Requires documentation updates

Testing

Please describe the test(s) that you added and ran to verify your changes.

Checklist

• I have read the contribution guide recently

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 76.45%. Comparing base (03135b6) to head (5a8f4ab).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #582   +/-   ##
=======================================
  Coverage   76.45%   76.45%           
=======================================
  Files           9        9           
  Lines        3648     3648           
=======================================
  Hits         2789     2789           
  Misses        859      859           

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[mcbarton]

@Vipul-Cariappa @aaronj0 I am going to open the cppyy counterpart to this PR sometime next week. I will likely to be able to generate the needed suppression files, but lack the knowledge to interpret them once generated, so will need your help there to see if anything in there is problematic.