Fix any-approver rule migration job failure

Related issue: #32472 (closed)

Currently PopulateAnyApprovalRuleForMergeRequests job fails because MergeRequest#approvals_before_merge is integer contains a large value, but ApprovalMergeRequestRule#approvals_required which it's migrated into is smallint.

The jobs have been introduced in this merge request: !16121 (merged)

This MR adds a condition to the SELECT statement:

SELECT id, CASE WHEN approvals_before_merge > 32767 THEN 32767 ELSE approvals_before_merge END, created_at, updated_at, 4, 'All Members' FROM "merge_requests"
  WHERE (NOT EXISTS (SELECT 1 FROM approval_merge_request_rules WHERE approval_merge_request_rules.merge_request_id = merge_requests.id))
  AND "merge_requests"."id" BETWEEN 1 AND 8 AND (approvals_before_merge <> 0)

Even though the jobs have been run already, it makes sense to fix this code, since it's going to be run again on the clean up stage