Investigate db:check-schema slowdown

We’ve seen a steep increase of the db:check-schema job duration in gitlab-org/gitlab>. It rose from 12m average in Early June up to 24m last week. If it keeps growing linearly like this, the job will take 37 minutes at the end of this year, leading to the minimum pipelinetier-1 MR pipeline duration skyrocketing to about 47 minutes (from 34 minutes today).

Link to chart (internal): https://app.snowflake.com/ys68254/gitlab/w1llSSv7KoXV/chart

We need to figure out why this is increasing like this and how to solve it.