hil: zephyr: disable sysbuild

The nrf9160DK now builds with sysbuild by default. We don't need
sysbuild for the HIL tests, so we disable it.

Signed-off-by: Sam Friedman <sam@golioth.io>

.github/workflows/hil_test_zephyr.yml

@@ -108,7 +108,7 @@ jobs:
 
           for test in $(ls modules/lib/golioth-firmware-sdk/tests/hil/tests)
           do
-            west build -p -b ${{ inputs.west_board }} \
+            west build --no-sysbuild -p -b ${{ inputs.west_board }} \
               modules/lib/golioth-firmware-sdk/tests/hil/platform/zephyr \
               -- $EXTRA_BUILD_ARGS -DGOLIOTH_HIL_TEST=$test
             mv build/zephyr/${{ inputs.binary_name }} \