selftests/kselftest_harness: Add harness-selftest.expected to TEST_FILES

The harness-selftest.expected is not installed in INSTALL_PATH.
Attempting to execute harness-selftest.sh shows warning:

diff: ./kselftest_harness/harness-selftest.expected: No such file or
directory

Add harness-selftest.expected to TEST_FILES.

Link: https://lore.kernel.org/r/20250909082619.584470-1-yi1.lai@intel.com
Fixes: df82ffc ("selftests: harness: Add kselftest harness selftest")
Signed-off-by: Yi Lai <yi1.lai@intel.com>
Reviewed-by: Thomas Weißschuh <thomas.weissschuh@linutronix.de>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>

Author: laifryiee

tools/testing/selftests/kselftest_harness/Makefile

@@ -2,6 +2,7 @@
 
 TEST_GEN_PROGS_EXTENDED := harness-selftest
 TEST_PROGS := harness-selftest.sh
+TEST_FILES := harness-selftest.expected
 EXTRA_CLEAN := harness-selftest.seen
 
 include ../lib.mk