Update 2.13.6.md

Author: lrytz

releases/2.13.6.md

@@ -14,6 +14,7 @@ The Scala 2 team at Lightbend is pleased to announce the availability of Scala 2
 * Check `private[this]` members in override checking ([#9542](https://github.com/scala/scala/pull/9542))
 * More accurate outer checks in patterns ([#9504](https://github.com/scala/scala/pull/9504))
 * Allow renaming imports from `_root_` ([#9482](https://github.com/scala/scala/pull/9482)) by [@som-snytt](https://github.com/som-snytt)
+* Make more annotations extend `ConstantAnnotation` ([9336](https://github.com/scala/scala/pull/9336)) by [@BalmungSan](https://github.com/BalmungSan)
 * A number of syntax changes were added to simplify cross-building between Scala 2 and 3
   * Don't error (only warn) on symbol literals under `-Xsource:3` ([#9602](https://github.com/scala/scala/pull/9602))
   * Support writing `&` instead of `with` in types under `-Xsource:3` ([#9594](https://github.com/scala/scala/pull/9594))