Update template.py main.schema_identifier doesn't exist

src/ifcopenshell-python/ifcopenshell/template.py

@@ -65,7 +65,7 @@ DEFAULTS = {
     "application": lambda d: "IfcOpenShell-%s" % main.version,
     "application_version": lambda d: main.version,
     "project_globalid": lambda d: compress(uuid.uuid4().hex),
-    "schema_identifier": lambda d: main.schema_identifier,
+    "schema_identifier": lambda d: "IFC4",
     "timestamp": lambda d: int(time.time()),
     "timestring": lambda d: time.strftime("%Y-%m-%dT%H:%M:%S", time.gmtime(d.get("timestamp") or time.time())),
 }