chore: fix migration notes (#6458)

Naming one version was missed.

docs/docs/migration_notes.md

@@ -8,7 +8,7 @@ Aztec is in full-speed development. Literally every version breaks compatibility
 
 ## TBD
 
-### [Aztec.nr] Keys: Token note now stores an owner master nullifying public key hash instead of an owner address.
+### [Aztec.nr] Keys: Token note now stores an owner master nullifying public key hash instead of an owner address
 
 i.e.
 
@@ -23,6 +23,8 @@ struct TokenNote \{
 
 Computing the nullifier similarly changes to use this master nullifying public key hash.
 
+## 0.40.0
+
 ### [Aztec.nr] Debug logging
 
 The function `debug_log_array_with_prefix` has been removed. Use `debug_log_format` with `{}` instead. The special sequence `{}` will be replaced with the whole array. You can also use `{0}`, `{1}`, ... as usual with `debug_log_format`.