Python: Fix getArgumentForCall when using keyword arguments

Yikes :|

Author: RasmusWL

python/ql/src/semmle/python/objects/ObjectAPI.qll

@@ -363,7 +363,7 @@ class CallableValue extends Value {
             or
             exists(string name |
                 call.getArgByName(name) = result and
-                this.(PythonFunctionObjectInternal).getScope().getArg(n + offset).getName() = name
+                this.(PythonFunctionObjectInternal).getScope().getArg(n).getName() = name
             )
             or
             called instanceof BoundMethodObjectInternal and

python/ql/test/library-tests/PointsTo/calls/getArgumentForCall.expected

@@ -19,5 +19,5 @@
 | 40 | ControlFlowNode for f() | Function f | 0 | ControlFlowNode for IntegerLiteral |
 | 40 | ControlFlowNode for f() | Function f | 1 | ControlFlowNode for IntegerLiteral |
 | 40 | ControlFlowNode for f() | Function f | 2 | ControlFlowNode for IntegerLiteral |
-| 42 | ControlFlowNode for Attribute() | Function C.n | 0 | ControlFlowNode for IntegerLiteral |
 | 42 | ControlFlowNode for Attribute() | Function C.n | 0 | ControlFlowNode for c |
+| 42 | ControlFlowNode for Attribute() | Function C.n | 1 | ControlFlowNode for IntegerLiteral |