Java agent version changes to 2.21

Reflect our dependency changes

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=222988751

Author: hasaadi

build/jarjar.jar

@@ -29,7 +29,7 @@ public final class GcpDebugletVersion {
   public static final int MAJOR_VERSION = 2;
 
   /** Minor version of the agent. */
-  public static final int MINOR_VERSION = 20;
+  public static final int MINOR_VERSION = 21;
 
   /**
    * Debugger agent version string in the format of MAJOR.MINOR.