Description of problem:

`$argocd app set` command does not work with a multi source application

Workaround

None

Prerequisites (if any, like setup, operators/versions):

GitOps 1.13 RC

Steps to Reproduce

1. Log in to ArgoCD server with `argocd login` locally
2. Create an application with multiple sources
3. Run `argocd app set<app name> --source-position <index> --repo <repo value or any other flag and respective value>

Actual results:

From the eg I used

WARN[0002] Failed to invoke grpc call. Use flag --grpc-web in grpc calls. To avoid this warning message, use flag --grpc-web. 
FATA[0004] rpc error: code = InvalidArgument desc = application spec for quarkus is invalid: InvalidSpecError: repository not accessible: repositories not accessible: &Repository{Repo: "https://github.com/varshab1210/values-test.git", Type: "", Name: "", Project: ""}: repo client error while testing repository: rpc error: code = Unknown desc = error testing repository connectivity: failed to get index: 404 Not Found  

Expected results:

field specified should be overwritten by the new value

Reproducibility (Always/Intermittent/Only Once):

Always

Acceptance criteria: 

Expected result is met

Definition of Done:

Acceptance criteria is met

Build Details:

Additional info (Such as Logs, Screenshots, etc):

 *