perf: Avoid reusing previous migration steps

[juliusknorr]

When running an upgrade we have several stages that might trigger repair steps.

• doUpgrade has the main execution flow
• pre-upgrade repair steps Repair::getBeforeUpgradeRepairSteps()
• Do core upgrade
• Do app upgrade for each app that has a version changed
  • executeRepairSteps pre-migration
  • executeRepairSteps post-migration
  • setupLiveMigrations live-migration

The Repair class has no default migration steps and there are both a setRepair and addStep methods, however for the case when we upgrade an app we do not need to run core migrations again.

This fix will ensure that after running we always empty the list of repair steps stored in the Repair class instance.

I also checked usages and for all other places we tend to overwrite the array anyways.

Also if the app has no steps itself it would skip the core migrations still around before this change anyways.

Checklist

• Code is properly formatted
• Sign-off message is added to all commits
• Tests (unit, integration, api and/or acceptance) are included
• Screenshots before/after for front-end changes
• Documentation (manuals or wiki) has been updated or is not required
• Backports requested where applicable (ex: critical bugfixes)