github: restrict branch-triggers on specific branches

In #2997 it was pointed out the current branch-trigger matches more
branches than the release-branches. Retrict the match-pattern to only
cover release-branches

Also only trigger builds on the next-branch and not branches prefixed
with this name.

Link: https://github.com/freifunk-gluon/gluon/pull/2997#issuecomment-1771076385



Signed-off-by: David Bauer <mail@david-bauer.net>

.github/workflows/build-gluon.yml

@@ -3,8 +3,8 @@ on:
   push:
     branches:
       - master
-      - next*
-      - v20*
+      - next
+      - 'v20[2-9][0-9].[0-9].x'
   pull_request:
     types: [opened, synchronize, reopened]