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