Add a simple test for GIT_LFS_SKIP_PUSH
Add a simple test for GIT_LFS_SKIP_PUSH

This test is basically the same as the test for --dry-run except
dry run reports progress as if the push actually happened, while
GIT_LFS_SKIP_PUSH doesn’t print anything at all.

Signed-off-by: Andrej Shadura <3fe2fd1720211ac6f19ed41a7088067fb072e2ec@collabora.co.uk>

github/git-lfs,github/git-lfs,github/git-lfs