[stable/zed] Bump MCAPI to 0.21.1 (#1615)

This is an automated cherry-pick of #1609
/assign mnaser
diff --git a/images/magnum/Dockerfile b/images/magnum/Dockerfile
index 621ad9a..c7bd244 100644
--- a/images/magnum/Dockerfile
+++ b/images/magnum/Dockerfile
@@ -21,7 +21,7 @@
 pip3 install \
     --constraint /upper-constraints.txt \
         /src/magnum \
-        magnum-cluster-api==0.20.0
+        magnum-cluster-api==0.21.1
 EOF
 
 FROM registry.atmosphere.dev/library/openstack-python-runtime:${RELEASE}