github: separate concurrency group per event for kernel and packages

github: separate concurrency group per event for kernel and packages

Manual workflow_dispatch and push share the same ref on main, so
they previously landed in the same concurrency group
'Build Kernel-refs/heads/main' (and the equivalent for the packages
workflow). With cancel-in-progress: false for non-PR events, only
one run can be pending per group: a newer queued run cancels the
older pending one.

That made the manual trigger unreliable in both directions. A push
landing while a dispatch was queued displaced the dispatch (so the
ccache reseed never ran), and dispatching while a push was queued
displaced the push (so the legitimate per-commit build was lost).

Adding github.event_name to the concurrency group puts pushes,
dispatches, and pull_requests in separate buckets on the same ref,
so they no longer compete with each other.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>
Link: https://github.com/openwrt/openwrt/pull/23283
Signed-off-by: Christian Marangi <ansuelsmth@gmail.com>