Port #20190 to v3
Port #20190 to v3

Scrollspy test: Allow for async .then() in jQuery 3; fixes #20182

Instead of doing a new assert.async(), just do a single one for the entire test
and let the .then() be async as well.

df2k2/bootstrap,LuoSpark/bootstrap,antonaavik/bootstrap,LimetecBiotechnologies/bootstrap,Softdocs/bootstrap,antonaavik/bootstrap,aoimedia/bootstrap,FernandezR/bootstrap,michael-brade/bootstrap,bkrukowski/bootstrap,LimetecBiotechnologies/bootstrap,panvagil/bootstrap,scjang/ssss,seoulstore/ssss,hiersekornc/bootstrap,devsong/bootstrap,GerHobbelt/bootstrap,Jazzo/bootstrap,mdo/bootstrap,hbrls/bootstrap,OneZenD/gr8alpha,antonaavik/bootstrap,Jazzo/bootstrap,scjang/ssss,df2k2/bootstrap,JobsUnited/bootstrap,KM-MFG/bootstrap,mosoft521/bootstrap,aoimedia/bootstrap,GerHobbelt/bootstrap,OneZenD/gr8alpha,aoimedia/bootstrap,RanHoNg/bootstrap,RanHoNg/bootstrap,df2k2/bootstrap,292388900/bootstrap-1,JobsUnited/bootstrap,df2k2/bootstrap,patrickhlauke/bootstrap,KM-MFG/bootstrap,the-open-university/ouice-bootstrap,hiersekornc/bootstrap,RanHoNg/bootstrap,mosoft521/bootstrap,seoulstore/ssss,seoulstore/ssss,nanuclickity/bootstrap,nanuclickity/bootstrap,patrickhlauke/bootstrap,justincron/bootstrap,stone2310/bootstrap,OneZenD/gr8alpha,scjang/ssss,justincron/bootstrap,panvagil/bootstrap,gencer/bootstrap,devsong/bootstrap,FernandezR/bootstrap,monoblaine/bootstrap,algolia/bootstrap,algolia/bootstrap,mosoft521/bootstrap,OneZenD/gr8alpha,hbrls/bootstrap,JobsUnited/bootstrap,stone2310/bootstrap,michael-brade/bootstrap,devsong/bootstrap,292388900/bootstrap-1,seoulstore/ssss,LuoSpark/bootstrap,bo01ean/bootstrap,patrickhlauke/bootstrap,justincron/bootstrap,the-open-university/ouice-bootstrap,stone2310/bootstrap,FernandezR/bootstrap,panvagil/bootstrap,antonaavik/bootstrap,Jazzo/bootstrap,LimetecBiotechnologies/bootstrap,hiersekornc/bootstrap,mdo/bootstrap,GerHobbelt/bootstrap,gencer/bootstrap,Softdocs/bootstrap,scjang/ssss,monoblaine/bootstrap,justincron/bootstrap,hbrls/bootstrap,FernandezR/bootstrap,bo01ean/bootstrap,gencer/bootstrap,the-open-university/ouice-bootstrap,mdo/bootstrap,michael-brade/bootstrap,monoblaine/bootstrap,Softdocs/bootstrap,bo01ean/bootstrap,KM-MFG/bootstrap,algolia/bootstrap,nanuclickity/bootstrap,hiersekornc/bootstrap,hbrls/bootstrap,LuoSpark/bootstrap,bkrukowski/bootstrap