We have been happily using ArgoCD with public repositories for a while, but we've run into problems trying to connect ArgoCD to a private repository. We have an Application that looks like this:

apiVersion: argoproj.io/v1alpha1
kind: Application
metadata:
  name: example-app
  namespace: argocd
spec:
  destination:
    name: example-cluster
    namespace: open-cluster-management-agent
  project: ops
  source:
    path: .
    repoURL: ssh://git@github.com/example-org/example-repo.git
    targetRevision: HEAD
  syncPolicy:
    automated:
      prune: true
      selfHeal: true
    syncOptions:
    - Validate=false
    - ApplyOutOfSyncOnly=true

And a corresponding secret with the secret key that looks like this:

apiVersion: v1
metadata:
  labels:
    argocd.argoproj.io/secret-type: repository
  name: example-repo
  namespace: argocd
type: Opaque
stringData:
  sshPrivateKey: |
    -----BEGIN OPENSSH PRIVATE KEY-----
    ...
    -----END OPENSSH PRIVATE KEY-----
  url: ssh://git@github.com/example-org/example-repo.git
kind: Secret

ArgoCD fails to sync this app and shows the following error:

rpc error: code = Unknown desc = error creating SSH agent: "SSH agent
requested but SSH_AUTH_SOCK not-specified"

I understand what that's telling me, but I'm not sure how to correct the problem in the context of ArgoCD.