ProjectExplorer: Make RunWorkerPrivate::runControl const

It's not meant to ever change after contstruction.

Change-Id: I912b58dfb70b40c9763b902650d2c657c28ccc5c
Reviewed-by: Christian Stenger <christian.stenger@qt.io>

src/plugins/projectexplorer/runconfiguration.cpp

@@ -562,7 +562,7 @@ public:
 
     RunWorker *q;
     RunWorkerState state = RunWorkerState::Initialized;
-    QPointer<RunControl> runControl;
+    const QPointer<RunControl> runControl;
     QList<RunWorker *> startDependencies;
     QList<RunWorker *> stopDependencies;
     QString id;