Fix failing TestGitReceivePackSuccess
Fix failing TestGitReceivePackSuccess

After https://gitlab.com/gitlab-org/gitaly/-/merge_requests/4766
has been introduced, the test started fail because we basically
cancel the git-receive-pack after the output is received

This commit gracefully closes the connection to make the test
pass

gitlabhq/gitlab-shell,gitlabhq/gitlab-shell,gitlabhq/gitlab-shell