Merge branch 'ar/receive-pack-worktree-env'

The GIT_WORK_TREE variable prepared to invoke the push-to-checkout hook was leaking into the environment even when there was no hook used and broke the default push-to-deploy (i.e., let "git checkout" update the working tree only when the working tree is clean). * ar/receive-pack-worktree-env: receive-pack: fix updateInstead with core.worktree