gitserver: make errors to have pointer receivers
Created by: DaivikDave
Fixes #33099 @sourcegraph/repo-management
Test plan
Changing errors to have pointer receiver shouldn't break anything https://go.dev/blog/error-handling-and-go
Created by: DaivikDave
Fixes #33099 @sourcegraph/repo-management
Changing errors to have pointer receiver shouldn't break anything https://go.dev/blog/error-handling-and-go