Fix tests reporting in parallel execution (#1379)

* Fix tests reporting in parallel execution

Fix issue where parallel test execution was unable to track failed tests and inform about their number.

* Fix logic in tests.sh

tests/gdb-tests/tests.sh

@@ -111,9 +111,10 @@ run_test() {
         PWNDBG_LAUNCH_TEST="${test_case}" \
         PWNDBG_DISABLE_COLORS=1 \
         run_gdb "${gdb_args[@]}"
+    retval=$?
 
     if [ "$SERIAL" -ne 1 ]; then
-        exit $?
+        exit $retval
     fi
 }