Use git --autostash to preserve local changes on update

This requires git >= 2.6

BUG: 420933
2 jobs for work/dfaure/autostash in 2 minutes and 2 seconds (queued for 2 seconds)
latest
Status Job ID Name Coverage
  Test
passed #72241
smoke-test

00:02:01

passed #72240
unit-test

00:00:37