samples: boards: espressif: ulp: Add sysbuild property

Add proper sysbuild property to debug_ulp sample

Signed-off-by: Lucas Tamborrino <lucas.tamborrino@espressif.com>

Author: LucasTambor

samples/boards/espressif/ulp/lp_core/debug_ulp/sample.yaml

@@ -6,3 +6,4 @@ tests:
       - esp32c6_devkitc/esp32c6/hpcore
     tags:
       - samples
+    sysbuild: true