update_release_branch: Fix commit message and Zephyr OWNERS
update_release_branch: Fix commit message and Zephyr OWNERS

Allow the relevant commits portion of the commit message to be
optional (not used for the zephyr main/cmsis repos).

Also prune any top level Zephyr OWNERS file changes to
avoid conflicts with expected modified branch OWNERS file.

BUG=b:257145337
TEST=Run for nissa firmware branch
BRANCH=none

Signed-off-by: Andrew McRae <44ad1424cfc8411c96d9181798ca41ae55709dfb@google.com>
Change-Id: Ic38ff025d7d57a8f2439d535bebd55a5be12935c
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/ec/+/4022998
Code-Coverage: Zoss <345cf107e82c70959d46f59d98bddc98ce458aff@prod.google.com>
Reviewed-by: Aseda Aboagye <12c9b286316a940fd31c24070da5ab64cdd4d0e7@chromium.org>

coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec