Python: Fix missing global variable source nodes

In lieu of removing the offending flow (which would likely have
consequences for a lot of other tests), I opted to simply _include_
the relevant nodes directly.

python/ql/src/semmle/python/dataflow/new/internal/DataFlowPublic.qll

@@ -446,6 +446,8 @@ class LocalSourceNode extends Node {
   LocalSourceNode() {
     not simpleLocalFlowStep+(any(CfgNode n), this) and
     not this instanceof ModuleVariableNode
+    or
+    this = any(ModuleVariableNode mvn).getARead()
   }
 
   /** Holds if this `LocalSourceNode` can flow to `nodeTo` in one or more local flow steps. */