Add missing since on setCurrentlyInvokedFactoryMethod()

See gh-29326

Author: izeye

spring-beans/src/main/java/org/springframework/beans/factory/support/SimpleInstantiationStrategy.java

@@ -56,6 +56,7 @@ public static Method getCurrentlyInvokedFactoryMethod() {
 	/**
 	 * Set the factory method currently being invoked or {@code null} to reset.
 	 * @param method the factory method currently being invoked or {@code null}
+	 * @since 6.0
 	 */
 	public static void setCurrentlyInvokedFactoryMethod(@Nullable Method method) {
 		currentlyInvokedFactoryMethod.set(method);