Update rust to 1.86.0 (#11431)

We keep the practice of keeping the compiler up to date, pointing to the
latest release. This is done by many other projects in the Rust
ecosystem as well.

[Announcement blog
post](https://blog.rust-lang.org/2025/04/03/Rust-1.86.0.html).

Prior update was in #10914.

storage_controller/src/heartbeater.rs

@@ -253,7 +253,7 @@ impl HeartBeat<Node, PageserverState> for HeartbeaterTask<Node, PageserverState>
                 PageserverState::WarmingUp { .. } => {
                     warming_up += 1;
                 }
-                PageserverState::Offline { .. } => offline += 1,
+                PageserverState::Offline => offline += 1,
                 PageserverState::Available { .. } => {}
             }
         }
@@ -391,7 +391,7 @@ impl HeartBeat<Safekeeper, SafekeeperState> for HeartbeaterTask<Safekeeper, Safe
         let mut offline = 0;
         for state in new_state.values() {
             match state {
-                SafekeeperState::Offline { .. } => offline += 1,
+                SafekeeperState::Offline => offline += 1,
                 SafekeeperState::Available { .. } => {}
             }
         }

storage_controller/src/main.rs

@@ -283,10 +283,8 @@ impl Secrets {
     fn load_secret(cli: &Option<String>, env_name: &str) -> Option<String> {
         if let Some(v) = cli {
             Some(v.clone())
-        } else if let Ok(v) = std::env::var(env_name) {
-            Some(v)
         } else {
-            None
+            std::env::var(env_name).ok()
         }
     }
 }

storage_controller/src/tenant_shard.rs

@@ -622,7 +622,7 @@ impl TenantShard {
             .collect::<Vec<_>>();
 
         attached_locs.sort_by_key(|i| i.1);
-        if let Some((node_id, _gen)) = attached_locs.into_iter().last() {
+        if let Some((node_id, _gen)) = attached_locs.into_iter().next_back() {
             self.intent.set_attached(scheduler, Some(*node_id));
         }