Python: Fix test issues

Fixes the test failures that arose from making `ExtractedArgumentNode`
local.

For the consistency checks, we now explicitly exclude the
`ExtractedArgumentNode`s (now much more plentiful due to the
overapproximation) that don't have a corresponding `getCallArg` tuple.

For various queries/tests using `instanceof ArgumentNode`, we instead us
`isArgumentNode`, which explicitly filters out the ones for which
`isArgumentOf` doesn't hold (which, again, is the case for most of the
nodes in the overapproximation).

python/ql/consistency-queries/DataFlowConsistency.ql

@@ -26,6 +26,8 @@ private module Input implements InputSig<Location, PythonDataFlow> {
     or
     // TODO: Implement post-updates for **kwargs, see tests added in https://github.com/github/codeql/pull/14936
     exists(ArgumentPosition apos | n.argumentOf(_, apos) and apos.isDictSplat())
+    or
+    missingArgumentCallExclude(n)
   }
 
   predicate reverseReadExclude(Node n) {
@@ -134,6 +136,14 @@ private module Input implements InputSig<Location, PythonDataFlow> {
       other.getNode().getScope() = f
     )
   }
+
+  predicate missingArgumentCallExclude(ArgumentNode arg) {
+    // We overapproximate the argument nodes in order to not rely on the global `getCallArg`
+    // predicate.
+    // Because of this, we must exclude the cases where we have an approximation but no actual
+    // argument node.
+    arg = getCallArgApproximation() and not getCallArg(_, _, _, arg, _)
+  }
 }
 
 import MakeConsistency<Location, PythonDataFlow, PythonTaintTracking, Input>