ci: Fix usage of out-of-date Gitaly version

Our CI jobs are using the Gitaly service, where we pull in the "latest" tag. As it turns out though, "latest" is pointing to Gitaly v13.3.0-rc5, which is definitely not the latest version at this point in time. This is because CNG was converted to not use the "latest" tag anymore, but instead to use a tag called "master" in gitlab-org/build/CNG!519 (merged).

This MR fixes this by using the "master" tag instead. Furthermore, it fixes an incompatibility with Gitaly in the RawChanges RPC, where Gitaly tried to remove OldPath and NewPath. The change was reverted for now, but we should still convert the code to use OldPathBytes and NewPathBytes.