Merge branch 'ps/maintenance-geometric-default'

"git maintenance" starts using the "geometric" strategy by default. * ps/maintenance-geometric-default: builtin/maintenance: use "geometric" strategy by default t7900: prepare for switch of the default strategy t6500: explicitly use "gc" strategy t5510: explicitly use "gc" strategy t5400: explicitly use "gc" strategy t34xx: don't expire reflogs where it matters t: disable maintenance where we verify object database structure t: fix races caused by background maintenance