wait-for-deps: update pattern for structure.sql
Caused by gitlab-org/gitlab!27885 (merged)
This change was necessitated by the above MR.
Move to matching COPY "schema_migrations"
vs INSER INTO "schema_migrations"
as upstream codebase moved to this. Without this change, one would see
"Database Schema - current: 20200325183636, codebase: 0"