Merge branch '2.21' into 2.x

Author: cowtowncoder

release-notes/VERSION-2.x

@@ -11,6 +11,7 @@ Modules:
 === Releases ===
 ------------------------------------------------------------------------
 
+2.21.4 (28-May-2026)
 2.21.3 (28-Apr-2026)
 2.21.2 (20-Mar-2026)
 2.21.1 (22-Feb-2026)
@@ -44,6 +45,8 @@ No changes since 2.19.0
 #51: Unify testing structure/tools to JUnit5 [JSTEP-10]
  (contributed by Joo-Hyuk K)
 
+2.18.8 (28-May-2026)
+2.18.7 (24-Apr-2026)
 2.18.6 (22-Feb-2026)
 2.18.5 (27-Oct-2025)
 2.18.4 (05-May-2025)