Git: BranchModel: Guard against detaching QList

Change-Id: Ia55d2dd5c4c5a0320704f33688663e2f8954a4ff
Reviewed-by: Eike Ziller <eike.ziller@qt.io>
Reviewed-by: Orgad Shaneh <orgads@gmail.com>

src/plugins/git/branchmodel.cpp

@@ -967,7 +967,7 @@ void BranchModel::Private::updateAllUpstreamStatus(BranchNode *node)
         q->updateUpstreamStatus(node);
         return;
     }
-    for (BranchNode *child : node->children)
+    for (BranchNode *child : std::as_const(node->children))
         updateAllUpstreamStatus(child);
 }