Change retention to class

Author: Quinn-With-Two-Ns

nexus-sdk/src/main/java/io/nexusrpc/Experimental.java

@@ -7,6 +7,6 @@
  * notice. This annotation is inherited.
  */
 @Inherited
-@Retention(RetentionPolicy.RUNTIME)
+@Retention(RetentionPolicy.CLASS)
 @Target({ElementType.FIELD, ElementType.TYPE, ElementType.METHOD})
 public @interface Experimental {}