Fix flow_graph initialization for 3.15

Summary: The 3.15 static compiler was picking up the wrong flow graph implementation. This caused it to be broken w/ the recent prologue changes.

Reviewed By: yoney

Differential Revision: D92118520

fbshipit-source-id: 434caa3e7bc6ee8a0bc5a94424ac413a15d6e402

Author: DinoV

cinderx/PythonLib/cinderx/compiler/static/__init__.py

@@ -1391,7 +1391,7 @@ def emit_load_static_method(
 
 
 class Static315CodeGenerator(Static314CodeGenerator, CinderCodeGenerator315):
-    pass
+    flow_graph = PyFlowGraph315
 
 
 if sys.version_info >= (3, 15):