chore: add older Julia versions

[ianna]

No description provided.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 73.83%. Comparing base (d11e61d) to head (5ffddf6).
Report is 3 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #70      +/-   ##
==========================================
- Coverage   74.06%   73.83%   -0.24%     
==========================================
  Files           4        4              
  Lines        1666     1605      -61     
==========================================
- Hits         1234     1185      -49     
+ Misses        432      420      -12     

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

[ianna]

Starting from Julia 1.8 and continuing in subsequent versions such as 1.9, this restriction has been lifted, allowing the declaration of const fields within mutable structs without raising an error.