samples: wifi: shell: Correct the options for scan_only build

In scan_only build we need to override the sysbuild config option
as well. By default it gets set to SB_CONFIG_WIFI_NRF70_SYSTEM_MODE
which enables supplicant. Overriding this with
SB_CONFIG_WIFI_NRF70_SCAN_ONLY fixes this.

Signed-off-by: Ravi Dondaputi <[email protected]>

Author: rado17

Diff for: samples/wifi/shell/sample.yaml

@@ -196,7 +196,7 @@ tests:
     build_only: true
     extra_args:
       - EXTRA_CONF_FILE=overlay-scan-only.conf
-      - CONFIG_WIFI_NM_WPA_SUPPLICANT=n
+      - SB_CONFIG_WIFI_NRF70_SCAN_ONLY=y
     platform_allow:
       - thingy91x/nrf9151/ns
     tags: