This updates Gitaly's latest Protocol Buffer definitions, which were
last updated in Feburary 2020, with the latest version of Gitaly. This
is done to ensure the definitions are in sync with Workhorse
(https://gitlab.com/gitlab-org/gitlab-workhorse/-/merge_requests/619)
and Gitaly.

Because we started tagging Gitaly versions `v13.x.x` instead of
`v1.x.x`, `go get` refuses to update the Gitaly module using the latest
tag or SHA (https://gitlab.com/gitlab-org/gitaly/-/issues/3177).  Go
tries to enforce semantic compatibility by requiring the use of module
paths (e.g. `m/v13`), and Gitaly doesn't adhere to this scheme.

To workaround this issue, we use the replace directive
(https://github.com/golang/go/wiki/Modules#when-should-i-use-the-replace-directive):

```
go mod edit -replace gitlab.com/gitlab-org/gitaly=gitlab.com/gitlab-org/gitaly@3f5e218def93024f3aafe590c22cd1b29f744105
```