Update example in folds.jl

[abhro]

Update language tags for syntax highlighting (julia -> julia-repl) and update Array type names to match newer Julia

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 84.57%. Comparing base (4067267) to head (2a77bac).
⚠️ Report is 8 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #207      +/-   ##
==========================================
- Coverage   84.93%   84.57%   -0.37%     
==========================================
  Files          15       15              
  Lines         697      687      -10     
==========================================
- Hits          592      581      -11     
- Misses        105      106       +1     

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