Aura: Ensure we are building on each relay chain fork

cumulus/client/consensus/aura/src/collators/basic.rs

@@ -138,6 +138,7 @@ where
  };
 
  let mut last_processed_slot = 0;
+ let mut last_relay_chain_block = Default::default();
 
  while let Some(request) = collation_requests.next().await {
  macro_rules! reject_with_error {
@@ -215,11 +216,13 @@ where
  //
  // Most parachains currently run with 12 seconds slots and thus, they would try to
  // produce multiple blocks per slot which very likely would fail on chain. Thus, we have
- // this "hack" to only produce on block per slot.
+ // this "hack" to only produce on block per slot per relay chain fork.
  //
  // With https://github.com/paritytech/polkadot-sdk/issues/3168 this implementation will be
  // obsolete and also the underlying issue will be fixed.
- if last_processed_slot >= *claim.slot() {
+ if last_processed_slot >= *claim.slot() &&
+ last_relay_chain_block > *relay_parent_header.number()
+ {
  continue
  }
 
@@ -261,6 +264,7 @@ where
  }
 
  last_processed_slot = *claim.slot();
+ last_relay_chain_block = *relay_parent_header.number();
  }
  }
 }