Fix demo links

[dmathieu]

Those two demo services have been renamed.

• [product-catalog] rename productcatalogservice to product-catalog opentelemetry-demo#1864
• [checkout] rename checkoutservice to checkout opentelemetry-demo#1867

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 82.2%. Comparing base (4a87cfe) to head (933d5a8).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##            main   #6160     +/-   ##
=======================================
- Coverage   82.2%   82.2%   -0.1%     
=======================================
  Files        273     273             
  Lines      23674   23674             
=======================================
- Hits       19478   19476      -2     
- Misses      3849    3851      +2     
  Partials     347     347             

see 1 file with indirect coverage changes

[MrAlias]

I plan to merge this early. It is a trivial docs fix that is going to fix the CI builds for other PRs.