Set the -e option to ensure this script fails on any unexpected errors.

Without this change, the kernel build may continue running with an
incorrect string in include/config/kernel.release.

Currently, try_tag() returns 1 when the expected tag is not found as an
ancestor, but this is a case where the script should continue.

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>