spec: Fix finding Git binaries in Gitaly setup helper

The Gitaly setup helper tries to verify that all required binaries are installed in case Gitaly fails to come up correctly. These checks also verify that Git binaries are in place, and if they're not we'll print a warning that they're missing. The check has gone stale though: Gitaly is nowadays installing versioned Git binaries, so there is no single gitaly-git binary anymore but instead version-suffixed binaries called gitaly-git-v*.

Fix the check by instead verifying that there is any version-suffixed Git binary in the expected location.