minor symfony#9613 [Workflow] Use subject to fetch state_machine (Matth--)

This PR was merged into the 4.0 branch.

Discussion
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[Workflow] Use subject to fetch state_machine

Not using the subject to fetch the stateMachine will throw an ErrorException  because the first argument passed to the get-method is a string and not an object.

Commits
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279a9c1 [Workflow] Use subject to fetch state_machine

Author: javiereguiluz

workflow/state-machines.rst

@@ -205,9 +205,9 @@ you can get this state machine by injecting the Workflow registry service::
             $this->workflows = $workflows;
         }
 
-        public function someMethod()
+        public function someMethod($subject)
         {
-            $stateMachine = $this->workflows->get('pull_request');
+            $stateMachine = $this->workflows->get($subject, 'pull_request');
             // ...
         }