Python: Fix tests by managing local sources

`API::Node::getAwaited` is restriced to local sources

Author: yoff

python/ql/lib/semmle/python/dataflow/new/internal/DataFlowPrivate.qll

@@ -175,6 +175,19 @@ module EssaFlow {
       contextManager.strictlyDominates(var)
     )
     or
+    // Async with var definition
+    //  `async with f(42) as x:`
+    //  nodeFrom is `x`, cfg node
+    //  nodeTo is `x`, essa var
+    //
+    // This makes the cfg node the local source of the awaited value.
+    exists(With with, ControlFlowNode var |
+      nodeFrom.(CfgNode).getNode() = var and
+      nodeTo.(EssaNode).getVar().getDefinition().(WithDefinition).getDefiningNode() = var and
+      with.getOptionalVars() = var.getNode() and
+      with.isAsync()
+    )
+    or
     // Parameter definition
     //   `def foo(x):`
     //   nodeFrom is `x`, cfgNode