Py3: fix warning: missing field 'tp_print' initializer [-Wmissing-field-initializers]

This warning is only specific to Py3.8. See https://docs.python.org/3/c-api/typeobj.html

src/Tools/generateTemplates/templateClassPyExport.py

@@ -366,8 +366,12 @@ PyTypeObject @self.export.Name@::Type = {
 #if PY_MAJOR_VERSION >= 3
     ,0                                                /*tp_finalize */
 #endif
-#if PY_VERSION_HEX >= 0x03080000
+#if PY_VERSION_HEX >= 0x03090000
     ,0                                                /*tp_vectorcall */
+#elif PY_VERSION_HEX >= 0x03080000
+    ,0                                                /*tp_vectorcall */
+    /* bpo-37250: kept for backwards compatibility in CPython 3.8 only */
+    ,0                                                /*tp_print */
 #endif
 };