fix(migration): Check if column exits before adding it

[solracsf]

• Resolves: [Bug]: Exception: Database error when running migration The column "scheduled_at" on table "oc_taskprocessing_tasks" already exists. #48372

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)

[solracsf]

/backport to stable30

[szaimen]

Makes sense! Can we somehow add a test for this so that such an if clause is never forgotten?

[joshtrichards]

Check makes sense, but I don't understand the state people are ending up in in that bug report: upgrading from v29 directly shouldn't have that column anyhow.

[joshtrichards]

Makes sense! Can we somehow add a test for this so that such an if clause is never forgotten?

Integration testing focused on the the upgrade path should catch these (which we don't have AFAIK). Particularly if we had a matrix covering major->major, beta->major, rc->major, etc.

[solracsf]

Makes sense! Can we somehow add a test for this so that such an if clause is never forgotten?

Integration testing focused on the the upgrade path should catch these (which we don't have AFAIK). Particularly if we had a matrix covering major->major, beta->major, rc->major, etc.

Yet this is out of the scope of this specific PR, I fully agree on this.