toxgen: Make it clearer which suites can be migrated

[sentrivana]

...also, cohere was in the IGNORE list twice, apparently.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 79.56%. Comparing base (d394ef6) to head (9ff1309).
Report is 1 commits behind head on master.

✅ All tests successful. No failed tests found.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #4196      +/-   ##
==========================================
+ Coverage   79.52%   79.56%   +0.04%     
==========================================
  Files         141      141              
  Lines       15738    15738              
  Branches     2675     2675              
==========================================
+ Hits        12515    12522       +7     
+ Misses       2376     2369       -7     
  Partials      847      847              

see 2 files with indirect coverage changes