zcbor: The tests are using invalid platforms

[nandojve]

Describe the bug

The zcbor tests are using invalid platforms which can break twister to collect tests.

Example:
https://github.com/zephyrproject-rtos/zcbor/blob/9b07780aca6fb21f82a241ba386ad9b379809337/tests/decode/test2_suit/testcase.yaml#L3

Regression

• This is a regression.

Steps to reproduce

when using zcbor in some project go to zcbor folder and try to run twister:

zcbor$ west twister -T .
INFO    - Using Ninja..
INFO    - Zephyr version: fd753fb95d06
INFO    - Using 'zephyr' toolchain.
ERROR   - platform_allow in zcbor.decode.test5_corner_cases - unrecognized platform - native_posix native_posix/native/64 mps2/an521/cpu0 qemu_malta/qemu_malta/be

Relevant log output

Impact

Showstopper – Prevents release or major functionality; system unusable.

Environment

• OS: Linux
• Toolchain Zephyr SDK 0.17.4
• mainline 9a0e8a4

Additional Context

No response