chore(bukkit/paper): Update testing server versions

Author: jpenilla

examples/example-bukkit/build.gradle.kts

@@ -50,7 +50,7 @@ tasks {
         8 to setOf("1.8.8"),
         11 to setOf("1.9.4", "1.10.2", "1.11.2"),
         17 to setOf("1.12.2", "1.13.2", "1.14.4", "1.15.2", "1.16.5", "1.17.1", "1.18.2", "1.19.4", "1.20.4"),
-        21 to setOf("1.20.6")
+        21 to setOf("1.20.6", "1.21")
     )
 
     runServer {

examples/example-paper/build.gradle.kts

@@ -47,7 +47,7 @@ tasks {
     }
 
     val runVersions = mapOf(
-        21 to setOf("1.20.6"),
+        21 to setOf("1.20.6", "1.21"),
     )
 
     runServer {