Switch to Entity.sendSystemMessage for chat output

displayClientMessage(Component, boolean) was removed from LocalPlayer
in 26.2. sendSystemMessage(Component) is inherited from Entity, has
been part of Mojang's public API since 1.19, and LocalPlayer overrides
it to route the message into the local chat hud, which is exactly the
behaviour we want.

src/client/java/ru/nevetime/clientirc/ClientIrcMod.java

@@ -113,7 +113,7 @@ public final class ClientIrcMod implements ClientModInitializer {
         }
         client.execute(() -> {
             if (client.player != null) {
-                client.player.displayClientMessage(text, false);
+                client.player.sendSystemMessage(text);
             } else {
                 LOGGER.info(text.getString());
             }