selftests: clone3: clone3: add case CLONE3_ARGS_NO_TEST

selftests: clone3: clone3: add case CLONE3_ARGS_NO_TEST

BugLink: https://bugs.launchpad.net/bugs/1959376
[ Upstream commit a531b0c23c0fc68ad758cc31a74cf612a4dafeb0 ]

Building selftests/clone3 with clang warns about enumeration not handled
in switch case:

clone3.c:54:10: warning: enumeration value 'CLONE3_ARGS_NO_TEST' not handled in switch [-Wswitch]
        switch (test_mode) {
                ^

Add the missing switch case with a comment.

Fixes: 17a810699c18 ("selftests: add tests for clone3()")
Signed-off-by: Anders Roxell <anders.roxell@linaro.org>
Acked-by: Christian Brauner <christian.brauner@ubuntu.com>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Paolo Pisati <paolo.pisati@canonical.com>