crypto: expose InboundGroupSession.sender_data

We need write access to this in the integration tests

crates/matrix-sdk-crypto/src/olm/group_sessions/inbound.rs

@@ -127,7 +127,7 @@ pub struct InboundGroupSession {
     /// the session, or, if we can use that device information to find the
     /// sender's cross-signing identity, holds the user ID and cross-signing
     /// key.
-    pub(crate) sender_data: SenderData,
+    pub sender_data: SenderData,
 
     /// The Room this GroupSession belongs to
     pub room_id: OwnedRoomId,