imgtool: Install imgtool dependencies in zephyr-build

Install imgtool dependencies before twister tests in zephyr-build to fix
failing ci job due to ImportError, originating from missing new types
added in cryptography library version 40.0.0.

Signed-off-by: Rustam Ismayilov <rustam.ismayilov@arm.com>
Change-Id: I1e4ca88a4a0329a198290f6e1917c139c30abc4f

Author: rustammendel

.github/workflows/zephyr_build.yaml

@@ -1,4 +1,5 @@
 # Copyright (c) 2022-2023 Nordic Semiconductor ASA
+# Copyright (c) 2024, Arm Limited
 # SPDX-License-Identifier: Apache-2.0
 
 name: Build Zephyr samples with Twister
@@ -91,6 +92,7 @@ jobs:
           export ZEPHYR_TOOLCHAIN_VARIANT=zephyr
           echo "Using Zephyr version: ${{ env.ZEPHYR_VERSION }}"
           echo "Using Mcuboot version: ${{ env.MCUBOOT_VERSION }}"
+          pip install -r ../bootloader/mcuboot/scripts/requirements.txt
           ./scripts/twister --inline-logs -v -N -M --integration --overflow-as-errors --retry-failed 2 ${test_paths}
 
       - name: Upload Tests Results