test3026: disable valgrind
    
    It fails on x86_64 with:
    ```
     Use --max-threads=INT to specify a larger number of threads
     and rerun valgrind
     valgrind: the 'impossible' happened:
        Max number of threads is too low
     host stacktrace:
     ==174357==    at 0x58042F5A: ??? (in /usr/libexec/valgrind/memcheck-amd64-linux)
     ==174357==    by 0x58043087: ??? (in /usr/libexec/valgrind/memcheck-amd64-linux)
     ==174357==    by 0x580432EF: ??? (in /usr/libexec/valgrind/memcheck-amd64-linux)
     ==174357==    by 0x58043310: ??? (in /usr/libexec/valgrind/memcheck-amd64-linux)
     ==174357==    by 0x58099E77: ??? (in /usr/libexec/valgrind/memcheck-amd64-linux)
     ==174357==    by 0x580E67E9: ??? (in /usr/libexec/valgrind/memcheck-amd64-linux)
     ==174357==    by 0x5809D59D: ??? (in /usr/libexec/valgrind/memcheck-amd64-linux)
     ==174357==    by 0x5809901A: ??? (in /usr/libexec/valgrind/memcheck-amd64-linux)
     ==174357==    by 0x5809B0B6: ??? (in /usr/libexec/valgrind/memcheck-amd64-linux)
     ==174357==    by 0x580E4050: ??? (in /usr/libexec/valgrind/memcheck-amd64-linux)
     sched status:
       running_tid=1
     Thread 1: status = VgTs_Runnable syscall 56 (lwpid 174357)
     ==174357==    at 0x4A07816: clone (in /usr/lib64/libc.so.6)
     ==174357==    by 0x4A08720: __clone_internal (in /usr/lib64/libc.so.6)
     ==174357==    by 0x4987ACF: create_thread (in /usr/lib64/libc.so.6)
     ==174357==    by 0x49885F6: pthread_create@@GLIBC_2.34 (in /usr/lib64/libc.so.6)
     ==174357==    by 0x1093B5: test.part.0 (lib3026.c:64)
     ==174357==    by 0x492454F: (below main) (in /usr/lib64/libc.so.6)
     client stack range: [0x1FFEFFC000 0x1FFF000FFF] client SP: 0x1FFEFFC998
     valgrind stack range: [0x1002BAA000 0x1002CA9FFF] top usage: 11728 of 1048576
    [...]
    ```