8288994: Incorrect @since tags for @value update in JDK-8286101

Reviewed-by: darcy, prappo

src/jdk.compiler/share/classes/com/sun/source/doctree/ValueTree.java

@@ -48,7 +48,7 @@ public interface ValueTree extends InlineTagTree {
      * @return the format string
      *
      * @implSpec This implementation returns {@code null}.
-     * @since 19
+     * @since 20
      */
     default TextTree getFormat() {
         return null;

src/jdk.compiler/share/classes/com/sun/source/util/DocTreeFactory.java

@@ -420,7 +420,7 @@ public interface DocTreeFactory {
      * @return a {@code ValueTree} object
      *
      * @implSpec This implementation calls {@link #newValueTree(ReferenceTree) newValueTree(ref)}.
-     * @since 19
+     * @since 20
      */
     default ValueTree newValueTree(TextTree format, ReferenceTree ref) {
         return newValueTree(ref);