Resolve issue when git operations over ssh were failing to proxy to primary

What does this MR do and why?

Fixes an issue on git operations over SSH on secondary sites. Tests with flexible mocking allowed the code to be tested calling the method as a class method, but it is an instance method.

References

#549748 (closed)

How to set up and validate locally

Execute git operations over SSH on a secondary site

MR acceptance checklist

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

Related to #549748 (closed)