actor_mesh: fix lint

Summary:
fix
```lang=text,counterexample
warning: using `.deref()` on a double reference, which returns `&ProcMesh` instead of dereferencing the inner type
  --> hyperactor_mesh/src/actor_mesh.rs:60:35
   |
60 |             Self::Borrowed(p) => p.deref(),
   |                                   ^^^^^^^^
   |
   = note: `#[warn(suspicious_double_ref_op)]` on by default
```

Reviewed By: dulinriley

Differential Revision: D75151288

fbshipit-source-id: 788bdfd2587af70de453cc1f2fb8a9eeb86937e5

Author: shayne-fletcher

hyperactor_mesh/src/actor_mesh.rs

@@ -57,7 +57,7 @@ impl Deref for ProcMeshRef<'_> {
     fn deref(&self) -> &Self::Target {
         match self {
             Self::Shared(p) => p,
-            Self::Borrowed(p) => p.deref(),
+            Self::Borrowed(p) => p, // p: &ProcMesh
         }
     }
 }