[CI] Upgrade to conan 2.21.0 for conanfile_latest

[marcalff]

Fixes #3702

Changes

Please provide a brief description of the changes here.

• Upgrade conan to 2.21.0 for install tests with conanfile_latest

For significant contributions please make sure you have completed the following items:

• CHANGELOG.md updated for non-trivial changes
• Unit tests have been added
• Changes in public API reviewed

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 89.95%. Comparing base (50942ba) to head (b3a304b).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3703      +/-   ##
==========================================
+ Coverage   89.94%   89.95%   +0.02%     
==========================================
  Files         225      225              
  Lines        7273     7273              
==========================================
+ Hits         6541     6542       +1     
+ Misses        732      731       -1     

see 1 file with indirect coverage changes

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[dbarker]

Looks good. Thanks!