tests: net: wifi: exclude RW612 ethernet variant

Ethernet board variant was missed in commit 138e959 (tests: net:
wifi: exclude RW612 based boards), but is the sole variant that actually
was running this test. Exclude this variant only, since it cannot build
this test due to requiring binary blobs.

Signed-off-by: Daniel DeGrasse <[email protected]>

Author: danieldegrasse

tests/net/wifi/wifi_nm/testcase.yaml

@@ -8,5 +8,4 @@ tests:
       - CONFIG_NRF_WIFI_BUILD_ONLY_MODE=y
     tags: wifi
     platform_exclude:
-      - frdm_rw612 # Requires binary blobs to build
-      - rd_rw612_bga # Requires binary blobs to build
+      - rd_rw612_bga/rw612/ethernet # Requires binary blobs to build