Source gitlab (mysql) to old Omnibus (postgres): ERROR: relation "schema_migrations" already exists

How to Use GitLab Migrations
1

I am in need to migrate a legacy GIT source installation that uses MySQL, to a new server, where the same version of Gitlab is installed but now as Omnibus install (gitlab-ce-8.17.8-ce.0.el7.x86_64.rpm), which uses embedded PostgreSQL.

I followed these instructions: Upgrading from a non-Omnibus installation to an Omnibus installation | GitLab

  1. Created a backup on the old server
  2. Copied backup to new server
  3. Extracted MySQL.sql and converted it to PostgreSQL
  4. Replaced MySQL dump with PostgreSQL dump
  5. Started the import (gitlab-rake gitlab:backup:restore 1673253345_2023_01_09_gitlab_backup.tar)

This import fails after some time with the following output:

NOTICE:  CREATE TABLE / PRIMARY KEY will create implicit index "protected_branch_push_access_levels_pkey" for table "protected_branch_push_access_levels"
CREATE TABLE
INSERT 0 1020
NOTICE:  CREATE TABLE / PRIMARY KEY will create implicit index "protected_branches_pkey" for table "protected_branches"
CREATE TABLE
INSERT 0 1020
NOTICE:  CREATE TABLE / PRIMARY KEY will create implicit index "releases_pkey" for table "releases"
CREATE TABLE
NOTICE:  CREATE TABLE / PRIMARY KEY will create implicit index "routes_pkey" for table "routes"
NOTICE:  CREATE TABLE / UNIQUE will create implicit index "routes_path_key" for table "routes"
NOTICE:  CREATE TABLE / UNIQUE will create implicit index "routes_source_type_source_id_key" for table "routes"
CREATE TABLE
INSERT 0 638
ERROR:  relation "schema_migrations" already exists
ERROR:  current transaction is aborted, commands ignored until end of transaction block
ERROR:  current transaction is aborted, commands ignored until end of transaction block
ERROR:  current transaction is aborted, commands ignored until end of transaction block
ERROR:  current transaction is aborted, commands ignored until end of transaction block
ERROR:  current transaction is aborted, commands ignored until end of transaction block
ERROR:  current transaction is aborted, commands ignored until end of transaction block
ERROR:  current transaction is aborted, commands ignored until end of transaction block
ERROR:  current transaction is aborted, commands ignored until end of transaction block
ERROR:  current transaction is aborted, commands ignored until end of transaction block
ERROR:  current transaction is aborted, commands ignored until end of transaction block
ERROR:  current transaction is aborted, commands ignored until end of transaction block
ERROR:  current transaction is aborted, commands ignored until end of transaction block
ERROR:  current transaction is aborted, commands ignored until end of transaction block
ERROR:  current transaction is aborted, commands ignored until end of transaction block
ERROR:  current transaction is aborted, commands ignored until end of transaction block
ERROR:  current transaction is aborted, commands ignored until end of transaction block
ERROR:  current transaction is aborted, commands ignored until end of transaction block
ERROR:  current transaction is aborted, commands ignored until end of transaction block
ERROR:  current transaction is aborted, commands ignored until end of transaction block
ERROR:  current transaction is aborted, commands ignored until end of transaction block
ERROR:  current transaction is aborted, commands ignored until end of transaction block
ERROR:  current transaction is aborted, commands ignored until end of transaction block
ERROR:  current transaction is aborted, commands ignored until end of transaction block
ERROR:  current transaction is aborted, commands ignored until end of transaction block
ERROR:  current transaction is aborted, commands ignored until end of transaction block
ERROR:  current transaction is aborted, commands ignored until end of transaction block
ERROR:  current transaction is aborted, commands ignored until end of transaction block
ERROR:  current transaction is aborted, commands ignored until end of transaction block
ERROR:  current transaction is aborted, commands ignored until end of transaction block
ROLLBACK
START TRANSACTION
ERROR:  relation "application_settings" does not exist
ERROR:  current transaction is aborted, commands ignored until end of transaction block
ERROR:  current transaction is aborted, commands ignored until end of transaction block
ERROR:  current transaction is aborted, commands ignored until end of transaction block
ERROR:  current transaction is aborted, commands ignored until end of transaction block
ERROR:  current transaction is aborted, commands ignored until end of transaction block
ERROR:  current transaction is aborted, commands ignored until end of transaction block

Any help how I can fix this is very welcome!