fixes: https://github.com/coder/internal/issues/1179
The problem in that flake is that dRPC doensn't consistently return
`context.Canceled` if you make an RPC call and then cancel it: sometimes
it returns EOF.
Without this PR, if we get an EOF on one of the routines that uses the
agentapi connection, we tear down the whole connection and reconnect to
coderd --- even if we are in the middle of a graceful shutdown.
What happened in the linked flake is that writing stats failed with EOF,
which then caused us to reconnect and write the lifecycle "SHUTTING
DOWN" twice.
Spike Curtis
ce9e7ad909