Fixes: #39270
The latest zephyrprojectrtos/ci no longer sets ZEPHYR_SDK_INSTALL_DIR
in the environment and doesn't register the Zephyr-SDK as a CMake
package in the CMake package registry.
To ensure the the Zephyr SDK can be correctly discovered by
find_package(Zephyr-sdk) we add `/opt/toolchains` to the
CMAKE_PREFIX_PATH environment variable which is a list containing
additional search prefixes for the `find_package()` function.
Signed-off-by: Torsten Rasmussen <Torsten.Rasmussen@nordicsemi.no>
