scripts/requirements: bump imgtool to 2.0.0

Resolves incorrectly located `image_ok` tag in generated hex files when
CONFIG_MCUBOOT_GENERATE_CONFIRMED_IMAGE is used.

Fixes #64098

Signed-off-by: Abram Early <abram.early@gmail.com>
(cherry picked from commit 5dec4fcab8bee81d1557fd6693c5f536e99060af)
1 file changed