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.

safekeeper/src/receive_wal.rs

@@ -94,10 +94,10 @@ impl WalReceivers {
 
     /// Get reference to locked slot contents. Slot must exist (registered
     /// earlier).
-    fn get_slot<'a>(
-        self: &'a Arc<WalReceivers>,
+    fn get_slot(
+        self: &Arc<WalReceivers>,
         id: WalReceiverId,
-    ) -> MappedMutexGuard<'a, WalReceiverState> {
+    ) -> MappedMutexGuard<'_, WalReceiverState> {
         MutexGuard::map(self.mutex.lock(), |locked| {
             locked.slots[id]
                 .as_mut()

safekeeper/src/timeline.rs

@@ -699,7 +699,7 @@ impl Timeline {
     }
 
     /// Take a writing mutual exclusive lock on timeline shared_state.
-    pub async fn write_shared_state<'a>(self: &'a Arc<Self>) -> WriteGuardSharedState<'a> {
+    pub async fn write_shared_state(self: &Arc<Self>) -> WriteGuardSharedState<'_> {
         WriteGuardSharedState::new(self.clone(), self.mutex.write().await)
     }