tests: bsim: Fix command execution with quoted string

When running a bsim test where an option's argument is a quoted string,
using $@ to execute the arguments of the Execute function causes
incorrect quote handling.

To correctly pass all arguments, add extra quotes around $@. This
ensures that quoted strings remain intact when passed to the executable.

Signed-off-by: Pavel Vasilyev <pavel.vasilyev@nordicsemi.no>

tests/bsim/sh_common.source

@@ -13,7 +13,7 @@ BOARD="${BOARD:-nrf52_bsim/native}"
 BOARD_TS="${BOARD//\//_}"
 
 function run_in_background(){
-  $@ & _process_ids="$_process_ids $!"
+  "$@" & _process_ids="$_process_ids $!"
 }
 
 function wait_for_background_jobs(){
@@ -46,7 +46,7 @@ function Execute() {
   EXECUTE_TIMEOUT="${EXECUTE_TIMEOUT:-30}"
 
   check_program_exists $1
-  run_in_background timeout --kill-after=5 -v ${EXECUTE_TIMEOUT} $@
+  run_in_background timeout --kill-after=5 -v ${EXECUTE_TIMEOUT} "$@"
 }
 
 function _guess_test_relpath(){