toxgen: Migrate fastapi

[sentrivana]

With this we've migrated the whole Web 1 group, yay! So the whole -latest category is gone for Web 1, too.

Also removed some pytest.mark.asyncios on sync tests

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 80.31%. Comparing base (0851458) to head (7d88e99).
Report is 1 commits behind head on master.

✅ All tests successful. No failed tests found.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #4302      +/-   ##
==========================================
+ Coverage   80.30%   80.31%   +0.01%     
==========================================
  Files         142      142              
  Lines       15919    15919              
  Branches     2722     2722              
==========================================
+ Hits        12783    12786       +3     
+ Misses       2262     2261       -1     
+ Partials      874      872       -2     

see 2 files with indirect coverage changes