Increase the size to prevent running out of space when the number
of comma-separated groups is large. This can be the case when there
are a large number of merge commits in related changes.
The schema migration takes into account that the column might have
already been changed, in case anyone decides to do that manually on
an existing 2.12.x site.
Bug: Issue 4323
Change-Id: Icb3081b11e84f178516f650ff84acc6ee75045d3
6a7213456e