Fixed a regression when updating config messages

Doing a config push was working via `Atomic.wrappedValue` instead of `Atomic.mutate` - we need to use `Atomic.mutate` in this case because we want to block other threads from modifying the config while we are doing a push (otherwise it can crash due to data changing while generating the push payload)

SessionMessagingKit/LibSession/LibSession+SessionMessagingKit.swift

@@ -229,11 +229,10 @@ public extension LibSession {
         /// config while we are reading (which could result in crashes)
         return try existingDumpVariants
             .reduce(into: PendingChanges()) { result, variant in
-                guard
-                    let conf = dependencies.caches[.libSession]
+                try dependencies.caches[.libSession]
                     .config(for: variant, publicKey: publicKey)
-                        .wrappedValue
-                else { return }
+                    .mutate { conf in
+                        guard conf != nil else { return }
                         
                         // Check if the config needs to be pushed
                         guard config_needs_push(conf) else {
@@ -295,6 +294,7 @@ public extension LibSession {
                         )
                     }
             }
+    }
     
     static func markingAsPushed(
         seqNo: Int64,