storcon: fix AZ-driven tenant selection in chaos (#10443)

## Problem

In https://github.com/neondatabase/neon/pull/10438 I had got the
function for picking tenants backwards, and it was preferring to move
things _away_ from their preferred AZ.

## Summary of changes

- Fix condition in `is_attached_outside_preferred_az`

storage_controller/src/tenant_shard.rs

@@ -1806,7 +1806,7 @@ impl TenantShard {
                         .get(&node_id)
                         .expect("referenced node exists")
                         .get_availability_zone_id(),
-                ) == self.intent.preferred_az_id.as_ref()
+                ) != self.intent.preferred_az_id.as_ref()
             })
             .unwrap_or(false)
     }