nspawn: allow sched_rr_get_interval_time64 through seccomp filter
    
    We only allow a selected subset of syscalls from nspawn containers
    and don't list any time64 variants (needed for 32-bit arches when
    built using TIME_BITS=64, which is relatively new).
    
    We allow sched_rr_get_interval which cpython's test suite makes
    use of, but we don't allow sched_rr_get_interval_time64.
    
    The test failures when run in an arm32 nspawn container on an arm64 host
    were as follows:
    ```
    ======================================================================
    ERROR: test_sched_rr_get_interval (test.test_posix.PosixTester.test_sched_rr_get_interval)
    ----------------------------------------------------------------------
    Traceback (most recent call last):
      File "/var/tmp/portage/dev-lang/python-3.11.0_p1/work/Python-3.11.0/Lib/test/test_posix.py", line 1180, in test_sched_rr_get_interval
        interval = posix.sched_rr_get_interval(0)
                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    PermissionError: [Errno 1] Operation not permitted
    ```
    
    Then strace showed:
    ```
    sched_rr_get_interval_time64(0, 0xffbbd4a0) = -1 EPERM (Operation not permitted)
    ```
    
    This appears to be the only time64 syscall that isn't already included one of
    the sets listed in nspawn-seccomp.c that has a non-time64 variant. Checked
    over each of the time64 syscalls known to systemd and verified that none
    of the others had a non-time64-variant whitelisted in nspawn other than
    sched_rr_get_interval.
    
    Bug: https://bugs.gentoo.org/880131
    (cherry picked from commit b9e7f22c2d80930cad36ae53e66e42a2996dca4a)