samples: net: wpan(usb|serial): exclude thingy53_nrf5340_cpuapp_ns

This commit excludes thingy53_nrf5340_cpuapp_ns platform from building
wpanusb and wpan_serial samples. The platform doesn't support TF-M yet
and therefore the build is bound to fail.

Due to limitations of the filter functionality, a more generic approach
where _ns platforms without TF-M support would be excluded from the
build, for example:

filter: dt_chosen_enabled("zephyr,ieee802154") and
	CONFIG_NRF_SOC_SECURE_SUPPORTED

doesn't properly filter out the needed platforms. As a result,
platform_exclude syntax is used to specifically exclude the platform.

Signed-off-by: Jędrzej Ciupis <jedrzej.ciupis@nordicsemi.no>

samples/net/wpan_serial/sample.yaml

@@ -9,6 +9,7 @@ common:
 tests:
   sample.net.wpan.serial:
     filter: dt_chosen_enabled("zephyr,ieee802154")
+    platform_exclude: thingy53_nrf5340_cpuapp_ns
   sample.net.wpan_serial.frdm_cr20a:
     extra_args: SHIELD=frdm_cr20a
     platform_allow: frdm_k64f

samples/net/wpanusb/sample.yaml

@@ -9,6 +9,7 @@ common:
 tests:
   sample.net.wpanusb:
     filter: dt_chosen_enabled("zephyr,ieee802154")
+    platform_exclude: thingy53_nrf5340_cpuapp_ns
   sample.net.wpanusb_frdm_cr20a:
     extra_args: SHIELD=frdm_cr20a
     platform_allow: frdm_k64f