docs: Add release notes for v9.0.21

DIRACGrid CI · DIRACGrid CI · commit bb0da020e4fb · 2026-05-29T15:31:42.000Z
diff --git a/release.notes b/release.notes
@@ -1,3 +1,6 @@
+[v9.0.21]
+
+
 [v9.0.20]
 
 *WorkloadManagement
