Upgrade to lightning-kmp 1.8.4 (#123)

This is a bugfix release, the main change is ACINQ/lightning-kmp#718.

Author: pm47

buildSrc/src/main/kotlin/Versions.kt

@@ -1,6 +1,6 @@
 object Versions {
     val kotlin = "1.9.23"
-    val lightningKmp = "1.8.3"
+    val lightningKmp = "1.8.4"
     val sqlDelight = "2.0.1"
     val okio = "3.8.0"
     val clikt = "4.2.2"

src/commonMain/kotlin/fr/acinq/lightning/bin/Main.kt

@@ -92,7 +92,7 @@ class Phoenixd : CliktCommand() {
         .defaultLazy {
             when (chain) {
                 Chain.Mainnet -> MempoolSpaceClient.OfficialMempoolMainnet
-                Chain.Testnet3 -> MempoolSpaceClient.OfficialMempoolTestnet
+                Chain.Testnet3 -> MempoolSpaceClient.OfficialMempoolTestnet3
                 else -> error("unsupported chain")
             }
         }