side-data: add a test to check sidedata upgrade
We want to make sure that sidedata computed at commit time and during upgrade
are the same. To do so, we upgrade the repository in test-copies-chain-merge.t
since the file is checking all the special case that we need to catch. The
sidedata content in both case should be the same.
Differential Revision: https://phab.mercurial-scm.org/D9124