Downgrade spigot-api to 1.20.6 to restore compatibility with versions before 1.21

[riku6460]

This is caused by API changes introduced in https://hub.spigotmc.org/stash/projects/SPIGOT/repos/bukkit/commits/7983b966630a4224ff7a26e321d2369444d17978

[08:17:25 ERROR]: Could not pass event ItemSpawnEvent to AncientGates v2.7.1
java.lang.IncompatibleClassChangeError: Method 'org.bukkit.entity.Villager$Profession[] org.bukkit.entity.Villager$Profession.values()' must be Methodref constant
        at AncientGates.jar/org.mcteam.ancientgates.util.EntityUtil.<clinit>(EntityUtil.java:90) ~[AncientGates.jar:?]
        at AncientGates.jar/org.mcteam.ancientgates.listeners.PluginBlockListener.onItemSpawn(PluginBlockListener.java:282) ~[AncientGates.jar:?]
        at com.destroystokyo.paper.event.executor.asm.generated.GeneratedEventExecutor12.execute(Unknown Source) ~[?:?]
        at org.bukkit.plugin.EventExecutor$2.execute(EventExecutor.java:77) ~[paper-api-1.20.6-R0.1-SNAPSHOT.jar:?]
        at co.aikar.timings.TimedEventExecutor.execute(TimedEventExecutor.java:81) ~[paper-api-1.20.6-R0.1-SNAPSHOT.jar:1.20.6-151-a4f0f5c]
        at org.bukkit.plugin.RegisteredListener.callEvent(RegisteredListener.java:70) ~[paper-api-1.20.6-R0.1-SNAPSHOT.jar:?]
        at io.papermc.paper.plugin.manager.PaperEventManager.callEvent(PaperEventManager.java:54) ~[paper-1.20.6.jar:1.20.6-151-a4f0f5c]
        at io.papermc.paper.plugin.manager.PaperPluginManagerImpl.callEvent(PaperPluginManagerImpl.java:131) ~[paper-1.20.6.jar:1.20.6-151-a4f0f5c]
        at org.bukkit.plugin.SimplePluginManager.callEvent(SimplePluginManager.java:628) ~[paper-api-1.20.6-R0.1-SNAPSHOT.jar:?]
        at org.bukkit.craftbukkit.event.CraftEventFactory.callItemSpawnEvent(CraftEventFactory.java:815) ~[paper-1.20.6.jar:1.20.6-151-a4f0f5c]
        at org.bukkit.craftbukkit.event.CraftEventFactory.doEntityAddEventCalling(CraftEventFactory.java:695) ~[paper-1.20.6.jar:1.20.6-151-a4f0f5c]
        at net.minecraft.server.level.ServerLevel.addEntity(ServerLevel.java:1705) ~[paper-1.20.6.jar:1.20.6-151-a4f0f5c]
        at net.minecraft.server.level.ServerLevel.addFreshEntity(ServerLevel.java:1627) ~[paper-1.20.6.jar:1.20.6-151-a4f0f5c]
        at net.minecraft.server.level.ServerLevel.addFreshEntity(ServerLevel.java:1622) ~[paper-1.20.6.jar:1.20.6-151-a4f0f5c]
        at net.minecraft.server.level.ServerPlayer.drop(ServerPlayer.java:2542) ~[paper-1.20.6.jar:1.20.6-151-a4f0f5c]
        at net.minecraft.world.entity.player.Player.drop(Player.java:721) ~[paper-1.20.6.jar:1.20.6-151-a4f0f5c]
        at net.minecraft.world.entity.player.Player.drop(Player.java:715) ~[paper-1.20.6.jar:1.20.6-151-a4f0f5c]
        at net.minecraft.server.network.ServerGamePacketListenerImpl.handleSetCreativeModeSlot(ServerGamePacketListenerImpl.java:3413) ~[paper-1.20.6.jar:1.20.6-151-a4f0f5c]
        at net.minecraft.network.protocol.game.ServerboundSetCreativeModeSlotPacket.handle(ServerboundSetCreativeModeSlotPacket.java:30) ~[paper-1.20.6.jar:1.20.6-151-a4f0f5c]
        at net.minecraft.network.protocol.game.ServerboundSetCreativeModeSlotPacket.handle(ServerboundSetCreativeModeSlotPacket.java:20) ~[paper-1.20.6.jar:1.20.6-151-a4f0f5c]
        at net.minecraft.network.protocol.PacketUtils.lambda$ensureRunningOnSameThread$0(PacketUtils.java:55) ~[paper-1.20.6.jar:1.20.6-151-a4f0f5c]
        at net.minecraft.server.TickTask.run(TickTask.java:18) ~[paper-1.20.6.jar:1.20.6-151-a4f0f5c]
        at net.minecraft.util.thread.BlockableEventLoop.doRunTask(BlockableEventLoop.java:151) ~[paper-1.20.6.jar:1.20.6-151-a4f0f5c]
        at net.minecraft.util.thread.ReentrantBlockableEventLoop.doRunTask(ReentrantBlockableEventLoop.java:24) ~[paper-1.20.6.jar:1.20.6-151-a4f0f5c]
        at net.minecraft.server.MinecraftServer.doRunTask(MinecraftServer.java:1511) ~[paper-1.20.6.jar:1.20.6-151-a4f0f5c]
        at net.minecraft.server.MinecraftServer.doRunTask(MinecraftServer.java:195) ~[paper-1.20.6.jar:1.20.6-151-a4f0f5c]
        at net.minecraft.util.thread.BlockableEventLoop.pollTask(BlockableEventLoop.java:125) ~[paper-1.20.6.jar:1.20.6-151-a4f0f5c]
        at net.minecraft.server.MinecraftServer.pollTaskInternal(MinecraftServer.java:1488) ~[paper-1.20.6.jar:1.20.6-151-a4f0f5c]
        at net.minecraft.server.MinecraftServer.pollTask(MinecraftServer.java:1411) ~[paper-1.20.6.jar:1.20.6-151-a4f0f5c]
        at net.minecraft.util.thread.BlockableEventLoop.managedBlock(BlockableEventLoop.java:135) ~[paper-1.20.6.jar:1.20.6-151-a4f0f5c]
        at net.minecraft.server.MinecraftServer.waitUntilNextTick(MinecraftServer.java:1377) ~[paper-1.20.6.jar:1.20.6-151-a4f0f5c]
        at net.minecraft.server.MinecraftServer.runServer(MinecraftServer.java:1238) ~[paper-1.20.6.jar:1.20.6-151-a4f0f5c]
        at net.minecraft.server.MinecraftServer.lambda$spin$0(MinecraftServer.java:323) ~[paper-1.20.6.jar:1.20.6-151-a4f0f5c]
        at java.base/java.lang.Thread.run(Thread.java:1474) ~[?:?]