Sure, here's the code:
import org.bukkit.Bukkit;
import org.bukkit.entity.Player;
import org.bukkit.event.EventHandler;
import org.bukkit.event.Listener;
import org.bukkit.event.player.PlayerResourcePackStatusEvent;
import org.bukkit.plugin.java.JavaPlugin;

public class ResourcePackInvincibilityPlugin extends JavaPlugin implements Listener {

@Override
public void onEnable() {
Bukkit.getPluginManager().registerEvents(this, this);
getLogger().info("InvincibleResourcePackPlugin enabled!");
}

@Override
public void onDisable() {
getLogger().info("InvincibleResourcePackPlugin disabled!");
}

@EventHandler
public void onResourcePackStatus(PlayerResourcePackStatusEvent event) {
Player player = event.getPlayer();

if (event.getStatus() == PlayerResourcePackStatusEvent.Status.ACCEPTED) {
player.setInvulnerable(true);
} else if (event.getStatus() == PlayerResourcePackStatusEvent.Status.SUCCESSFULLY_LOADED) {
player.setInvulnerable(false);
}
}
}