tests: subsys: pm: power_mgmt: fix incorrect use of OVERLAY_CONFIG

Replace OVERLAY_CONFIG with CONF_FILE since no-device-pm.conf
contains an alternative configuration to the one in prj.conf

Signed-off-by: Abderrahmane Jarmouni <[email protected]>

Author: JarmouniA

tests/subsys/pm/power_mgmt/testcase.yaml

@@ -5,4 +5,4 @@ tests:
   pm.system: {}
   pm.system.no.device.pm:
     extra_args:
-      - EXTRA_CONF_FILE="no-device-pm.conf"
+      - CONF_FILE="no-device-pm.conf"