Update gitaly storage paths to not share same path

What does this MR do and why?

Updates the gitaly rails test setup to only have storages configured that the node itself is using.

• An example of where the current configuration will cause problems in the near future is described gitaly#5664 (comment 1783797955)

MR acceptance checklist

Please evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.

How to set up and validate locally

• All tests should pass