fix: IncompatibleClassChangeError w/ dynamic title update pre MC 1.21 (#735)

Author: DevNatan

gradle/libs.versions.toml

@@ -1,7 +1,10 @@
 [versions]
 jetbrains-annotations = "26.0.2"
-spigot = "1.21.5-R0.1-SNAPSHOT"
-paperSpigot = "1.21.5-R0.1-SNAPSHOT"
+# Do not update Spigot/Paper to 1.21, InventoryView changed from class to interface type
+# Dynamic Title Update feature throws IncompatibleClassChangeError due to that
+# Feel free to implement a workaround on InventoryUpdate.java if u need to use a 1.21+ specific API
+spigot = "1.20.6-R0.1-SNAPSHOT"
+paperSpigot = "1.20.6-R0.1-SNAPSHOT"
 junit = "5.12.2"
 mockito = "4.11.0"
 adventure-api = "4.19.0"