Fix gitaly-proto version for gitlab-ee v10.7.1

What does this MR do?

Updates the gitaly-proto version for gitlab-ee v10.7.1 from v0.94.0 to v0.96.0

Are there points in the code the reviewer needs to double check?

Why was this MR needed?

The GetSnapshot merge request originally updated the proto to v0.96.0, but just before merge, this was superceded by a commit to master that updated it to v0.97.0 - so no update hunk was picked to the 10.7 EE stable branch.

This MR fixes spec and production failures that will occur due to a dependency on missing constants and methods in the gitaly-proto gem.

It does not need to be merged to master, so I've set it to merge directly to the 10-7-stable-ee-patch-1 branch.