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

diff --cc t/t5319-multi-pack-index.sh
Simple merge

diff --cc t/t5331-pack-objects-stdin.sh
Simple merge

diff --cc t/t5500-fetch-pack.sh
Simple merge

diff --cc t/test-lib.sh
Simple merge