Mention callbacks introduced in v1.39.0

According to #10386 and #9884

docs/modules/account_validity_callbacks.md

@@ -9,6 +9,8 @@ The available account validity callbacks are:
 
 ### `is_user_expired`
 
+_First introduced in Synapse v1.39.0_
+
 ```python
 async def is_user_expired(user: str) -> Optional[bool]
 ```
@@ -29,6 +31,8 @@ any of the subsequent implementations of this callback.
 
 ### `on_user_registration`
 
+_First introduced in Synapse v1.39.0_
+
 ```python
 async def on_user_registration(user: str) -> None
 ```

docs/modules/third_party_rules_callbacks.md

@@ -10,6 +10,8 @@ The available third party rules callbacks are:
 
 ### `check_event_allowed`
 
+_First introduced in Synapse v1.39.0_
+
 ```python
 async def check_event_allowed(
     event: "synapse.events.EventBase",
@@ -51,6 +53,8 @@ any of the subsequent implementations of this callback.
 
 ### `on_create_room`
 
+_First introduced in Synapse v1.39.0_
+
 ```python
 async def on_create_room(
     requester: "synapse.types.Requester",
@@ -76,6 +80,8 @@ callback.
 
 ### `check_threepid_can_be_invited`
 
+_First introduced in Synapse v1.39.0_
+
 ```python
 async def check_threepid_can_be_invited(
     medium: str,
@@ -94,6 +100,8 @@ any of the subsequent implementations of this callback.
 
 ### `check_visibility_can_be_modified`
 
+_First introduced in Synapse v1.39.0_
+
 ```python
 async def check_visibility_can_be_modified(
     room_id: str,