Attempt to make scheduler tests less flaky

[mathialo]

Give the first run of the trigger test some time to finish, since the
scheduler doesn't allow multiple runs of the same task at the same time

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 75.27%. Comparing base (eaffda2) to head (6971086).
Report is 2 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #435      +/-   ##
==========================================
+ Coverage   75.22%   75.27%   +0.04%     
==========================================
  Files          42       42              
  Lines        3496     3499       +3     
==========================================
+ Hits         2630     2634       +4     
+ Misses        866      865       -1     

see 1 file with indirect coverage changes

🚀 New features to boost your workflow:

• ❄ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

[cemreyavuz]

risk review ok