Add generic XML syntax testing to a flow test

Adding it to one test is sufficient because we use the same loading logic across all flows.

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=239506003

docs/flows.md

@@ -785,6 +785,8 @@ A flow for an Epp "hello".
 
 ### Errors
 
+*   2001
+    *   Generic XML syntax error that can be thrown by any flow.
 
 ## HostCheckFlow