release 21.3.1

Author: gaborbernat

docs/changelog.rst

@@ -6,6 +6,17 @@
 
 .. towncrier release notes start
 
+**********************
+ v21.3.1 (2026-05-05)
+**********************
+
+Bugfixes - 21.3.1
+=================
+
+- Upgrade embedded wheels:
+
+  - pip to ``26.1.1`` from ``26.1`` (:issue:`3138`)
+
 **********************
  v21.3.0 (2026-04-27)
 **********************