CI: build Docker images for all release branches

This will also ensure that Docker images are created
for the release-2.0 branch, once this commit has been
merged into that branch.

Author: stsnel

.github/workflows/build-push-image.yml

@@ -5,8 +5,7 @@ on:
   push:
     branches:
       - 'development'
-      - 'release-1.9'
-      - 'release-1.10'
+      - 'release-[0-9]+.[0-9]+'
 
 jobs:
   push-image: