Run checks on v21.03 branch too (MR 3)

.ci/generate_page.sh

 #!/bin/sh -ex
 
-export BRANCHES="master v20.05"
+export BRANCHES="
+	master
+	v20.05
+	v21.03
+	"
 
 mkdir -p public
 

.gitlab-ci.yml

@@ -55,6 +55,17 @@ upstream-compat-v20.05:
     paths:
       - "*.check-passed"
 
+upstream-compat-v21.03:
+  stage: check
+  <<: *only-default
+  allow_failure: true
+  script:
+  - ./test_upstream_compat_setup.sh "v21.03"
+  artifacts:
+    when: always
+    paths:
+      - "*.check-passed"
+
 pages:
   stage: badge
   <<: *only-default