Hello 
Yes command failed too.
I have post log at: Output from Gitlab after passing from 14.2.7 -> 14.3.0 ($2402455) · Snippets · Snippets · GitLab
When I started Gitlab in Docker as gitlab/gitlab-ce:14.3.0-ce.0, I get the first log ( log_14.2.7_to_14.3.0.txt)
And by executing finalize background migrations (gitlab/gitlab-ce:14.2.7-ce.0 because 14.3.0 doesn’t start) - (Second log log_14.2.7_with_finalize_background_migration.txt)
Thanks in advance 
Have a good day
Cordially
Thomas S.