Allow Celo Cancun singer when requested

This makes all tests pass without additional changes in other places. I
hope we'll find a cleaner solution to handle this.

core/types/transaction_signing.go

@@ -69,12 +69,17 @@ func MakeSigner(config *params.ChainConfig, blockNumber *big.Int, blockTime uint
 // have the current block number available, use MakeSigner instead.
 func LatestSigner(config *params.ChainConfig) Signer {
 	if config.ChainID != nil {
+		if config.Cel2Time != nil {
+			if config.CancunTime != nil {
+				// This branch is only used in testing
+				return latestCeloSigner(config.ChainID, NewCancunSigner(config.ChainID))
+			} else {
+				return latestCeloSigner(config.ChainID, NewLondonSigner(config.ChainID))
+			}
+		}
 		if config.CancunTime != nil && !config.IsOptimism() {
 			return NewCancunSigner(config.ChainID)
 		}
-		if config.Cel2Time != nil {
-			return latestCeloSigner(config.ChainID, NewLondonSigner(config.ChainID))
-		}
 		if config.LondonBlock != nil {
 			return NewLondonSigner(config.ChainID)
 		}