Update secret.yaml

[fiskhest]

Causes a secret to be generated that has SB_USER set twice with the same value:

# Source: silverbullet/templates/secret.yaml
apiVersion: v1
kind: Secret
metadata:
  name: silverbullet
  labels:
    helm.sh/chart: silverbullet-0.4.0
    app.kubernetes.io/name: silverbullet
    app.kubernetes.io/instance: silverbullet
    app.kubernetes.io/version: "0.7.7"
    app.kubernetes.io/managed-by: Helm
type: Opaque
data:
  SB_USER: <redacted base64>
  SB_USER: <same value as above>