Use unique storages for setup of gitaly in rails tests
As described in gitlab-org/gitaly#5664 (comment 1783797955) the rails tests configuration should be updated to reflect a more realistic configuration.
While this setup appears to work today, it is preventing the usage of transactions in gitaly
The Rails tests are setting up two Gitaly processes and pointing both of them to the same storages. This is a bit non-sensical and it now fails with transactions as Gitaly acquires a lock on the entire storage to prevent concurrent modifications to it. Each of the Gitaly processes would need to have their own storages.