Add support for Java 21

By: md_5 <git@md-5.net>

paper-server/pom.xml

@@ -54,7 +54,7 @@
         <dependency>
             <groupId>org.ow2.asm</groupId>
             <artifactId>asm</artifactId>
-            <version>9.4</version>
+            <version>9.5</version>
             <scope>compile</scope>
         </dependency>
         <!-- Mojang depends -->

paper-server/src/main/java/org/bukkit/craftbukkit/Main.java

@@ -165,8 +165,8 @@ public class Main {
                 System.err.println("Unsupported Java detected (" + javaVersion + "). This version of Minecraft requires at least Java 17. Check your Java version with the command 'java -version'.");
                 return;
             }
-            if (javaVersion > 64.0) {
-                System.err.println("Unsupported Java detected (" + javaVersion + "). Only up to Java 20 is supported.");
+            if (javaVersion > 65.0) {
+                System.err.println("Unsupported Java detected (" + javaVersion + "). Only up to Java 21 is supported.");
                 return;
             }
             String javaVersionName = System.getProperty("java.version");