feat: enable open enums

Tested this doesn't regress chat in https://github.com/gleanwork/glean-api-client-examples

Author: david-hamilton-glean

.speakeasy/gen.yaml

@@ -59,7 +59,7 @@ python:
   flattenGlobalSecurity: true
   flattenRequests: true
   flatteningOrder: parameters-first
-  forwardCompatibleEnumsByDefault: false
+  forwardCompatibleEnumsByDefault: true
   forwardCompatibleUnionsByDefault: "false"
   imports:
     option: openapi