ListNamespace occasionally failed with error:"token signature is invalid"

[zhangcunli]

Describe the bug

1. I deploy dgraph cluster, 3 alpha node(v250.0.0-preview4)；
2. I use dgo sdk init client（v250.0.0-preview4）:

  dgo.WithACLCreds("groot", "password"),
  dgo.WithGrpcOption(grpc.WithTransportCredentials(insecure.NewCredentials())),
)```
3.But When I call the ListNamespace API endpoint, I occasionally get/receive the following error: "rpc error: code = Unknown desc = Non superadmin user cannot list namespaces. Authorize guardian of the galaxy, extracting jwt token, error:: extracting namespace from JWT: unable to parse jwt token: token signature is invalid: signature is invalid"

## To Reproduce
1. Init client:```client, err := dgo.NewRoundRobinClient([]string{"localhost:9080", "localhost:9080", "localhost:9080"},
  dgo.WithACLCreds("groot", "password"),
  dgo.WithGrpcOption(grpc.WithTransportCredentials(insecure.NewCredentials())),
)```
2.Multiple calls to the ListNamespace API endpoint.

## Expected behavior

I expect every call to the ListNamespace API endpoint to return a successful response consistently.

## Screenshots

## Environment

- OS: [macOS]
- Language [Go]
- Version [v250.0.0-preview4]

## Additional context

Add any other context about the problem here.

[linear]

DGR-896 ListNamespace occasionally failed with error:"token signature is invalid"