Remove unnecessary mut

[dakaizou]

Motivation

Since HealthReporter is already using RwLock:

tonic/tonic-health/src/server.rs

Line 36 in 72b0fd5

statuses: Arc<RwLock<HashMap<String, StatusPair>>>,

we can remove mutable reference here:

tonic/tonic-health/src/server.rs

Line 73 in 72b0fd5

pub async fn set_service_status<S>(&mut self, service_name: S, status: ServingStatus)

Or if we want to keep this interface, we can remove the RwLock.

Solution

Not using mutable reference.