Only scroll at the top of the infinite list on mount

There was an implicit dependency on the scroll handler that wasn't
correct, since it would trigger scroll-to-top at unexpected times.
Splitting the effect into two solves the issue at no cost.
1 job for dont-scroll-top-infinite-list in 5 minutes and 59 seconds (queued for 2 seconds)
Status Name Job ID Coverage
passed ci #1354021