tests: arch: arm: Disable l552ze in arm.swap.tz

Disabling nucleo_l552ze_q_ns from the test suite since there isn't
enough room to sign the image with the toolchain used in CI. This can
be reverted if changes are made to the nucleo_l552ze_q_ns platform to
enable enough room for the signing data.

Signed-off-by: Kevin Townsend <kevin.townsend@linaro.org>