Apply arc patches more forcefully
When arc applies a diff that's stacked on top of another one, it applies the full stack. However, it also edits the commit message, which changes the identifier of the base commit, which makes it fail to apply higher diffs.
Turning on the force flag allows stacks to apply properly.
Close #1445 (closed).
Test Plan
change applied manually on DCORE/tox; the rebuild of swh/devel/swh-core!53 (closed) succeeded.
Migrated from D1313 (view on Phabricator)