ci: trigger CI on rel-* branch pushes for tag protection rule (#1004)

The Release Tag ruleset requires test-and-build (ubuntu) to pass
before v* tags can be pushed, but CI previously only ran on main and
pull_request events. This caused rel-* version bump commits to fail
the tag protection check unless a workaround PR was opened.

Co-authored-by: openhands <openhands@all-hands.dev>

.github/workflows/ci.yml

@@ -5,6 +5,7 @@ on:
   push:
     branches:
       - main
+      - "rel-*"
   workflow_dispatch:
     inputs:
       pr_number: