agent: fix data race on inmemSink's token (#7707)
agent: fix data race on inmemSink's token (#7707)

* agent: fix data race on inmemSink's token

* use uber/atomic instead

quixoten/vault,rnaveiras/vault,hashicorp/vault,joelthompson/vault,quixoten/vault,hashicorp/vault,joelthompson/vault,hashicorp/vault,hartsock/vault,kingland/vault,rnaveiras/vault,kingland/vault,hartsock/vault,joelthompson/vault,hashicorp/vault,hartsock/vault,hashicorp/vault,rnaveiras/vault,hartsock/vault,kingland/vault,kingland/vault,quixoten/vault,joelthompson/vault,rnaveiras/vault,kingland/vault,hartsock/vault,quixoten/vault,hashicorp/vault,rnaveiras/vault