Build v2021pre images

Signed-off-by: Ritesh Raj Sarraf <rrs@debian.org>

.gitlab-ci.yml

 variables:
   osname: apertis
-  release: v2021dev3
+  release: "v2021pre"
 
 include:
   - /gitlab-ci/update-test-binaries.yaml

Jenkinsfile

 pipeline {
   environment {
-      release = "v2021dev3"
+      release = "v2021pre"
       branch = "apertis/${release}"
   }