Fix schema listing command in migration guide (Fission-AI#608)

Author: TabishB

docs/migration-guide.md

@@ -466,7 +466,7 @@ When determining which schema to use, OPSX checks in order:
 List all available schemas:
 
 ```bash
-openspec workflow schemas
+openspec schemas
 ```
 
 ### Custom Schemas
@@ -510,7 +510,7 @@ Check that your `rules:` keys match your schema's artifact IDs:
 Run this to see valid artifact IDs:
 
 ```bash
-openspec workflow schemas --json
+openspec schemas --json
 ```
 
 ### Config not being applied