This commit promotes all post_deploy migrations which existed in
Discourse v2.8.0 (timestamp <= 20220107014925).
This commit includes a fix to the promote_migrations script to promote
all migrations of the first version of the previous stable version. For
example, if the current stable version is v2.8.13, the version used as
a cutoff for promoting migrations is v2.8.0.
Bianca Nenciu