Fixes serial operations not running in FIFO order

Ensures AltStore is always the last app to be refreshed, which matters when AltStore needs to be resigned and reinstalled (such as when using AltDaemon on iOS 14).

AltStore/Managing Apps/AppManager.swift

@@ -1403,12 +1403,26 @@ private extension AppManager
     
     func run(_ operations: [Foundation.Operation], context: OperationContext?, requiresSerialQueue: Bool = false)
     {
+        // Reference to previous serial operation in context used to enforce FIFO,
+        // even if the operations become ready in a different order than submitted.
+        var previousSerialOperation: Foundation.Operation? = context?.operations.allObjects.filter { self.serialOperationQueue.operations.contains($0) }.last
+        
         for operation in operations
         {
             switch operation
             {
             case _ where requiresSerialQueue: fallthrough
-            case is InstallAppOperation, is RefreshAppOperation, is BackupAppOperation: self.serialOperationQueue.addOperation(operation)
+            case is InstallAppOperation, is RefreshAppOperation, is BackupAppOperation:
+                if let previousOperation = previousSerialOperation
+                {
+                    // Add dependency on previous serial operation to enforce FIFO.
+                    operation.addDependency(previousOperation)
+                }
+                
+                self.serialOperationQueue.addOperation(operation)
+                
+                previousSerialOperation = operation
+                
             default: self.operationQueue.addOperation(operation)
             }