Fix LFS uploads not working with git-lfs 2.5.0
git-lfs 2.5.0 now sets the Content-Type header instead of hard-coding it to application/octet-stream: https://github.com/git-lfs/git-lfs/pull/3137
To avoid this issue, we explicitly tell the client to use application/octet-stream.
Closes #49752 (closed)