docs: update mig notes release version (#11685)

Change to .md

Author: jzaki

docs/docs/migration_notes.md

@@ -6,7 +6,7 @@ keywords: [sandbox, aztec, notes, migration, updating, upgrading]
 
 Aztec is in full-speed development. Literally every version breaks compatibility with the previous ones. This page attempts to target errors and difficulties you might encounter when upgrading, and how to resolve them.
 
-## TBD
+## 0.73.0
 
 ### [Token, FPC] Moving fee-related complexity from the Token to the FPC