Don't fail if /home/git/repositories already exists in Gitaly container

The build is failing because registry.gitlab.com/gitlab-org/build/cng/gitaly:latest seems to have a directory at /home/git/repositories now

$ docker run registry.gitlab.com/gitlab-org/build/cng/gitaly:latest ls -lad /home/git/repositories
+ /scripts/set-config /etc/gitaly /etc/gitaly
Begin parsing .erb files from /etc/gitaly
+ exec ls -lad /home/git/repositories
drwxr-xr-x 2 git git 4096 Nov  6 20:47 /home/git/repositories