Disable a Travis-ci matrix run until Ubuntu bug resolved

[kozlovic]

gcc9 - Default - sanitize thread fails with following error:

CMake Error at /home/travis/deps/cmake-install/share/cmake-3.20/Modules/CMakeTestCCompiler.cmake:66 (message):
  The C compiler
    "/usr/bin/gcc-9"
  is not able to compile a simple test program.
  It fails with the following output:
    Change Dir: /home/travis/build/nats-io/nats.c/build/CMakeFiles/CMakeTmp

    Run Build Command(s):/usr/bin/make -f Makefile cmTC_613bf/fast && /usr/bin/make  -f CMakeFiles/cmTC_613bf.dir/build.make CMakeFiles/cmTC_613bf.dir/build
    make[1]: Entering directory '/home/travis/build/nats-io/nats.c/build/CMakeFiles/CMakeTmp'
    Building C object CMakeFiles/cmTC_613bf.dir/testCCompiler.c.o
    /usr/bin/gcc-9   -fsanitize=thread  -o CMakeFiles/cmTC_613bf.dir/testCCompiler.c.o -c /home/travis/build/nats-io/nats.c/build/CMakeFiles/CMakeTmp/testCCompiler.c
    Linking C executable cmTC_613bf
    /home/travis/deps/cmake-install/bin/cmake -E cmake_link_script CMakeFiles/cmTC_613bf.dir/link.txt --verbose=1
    /usr/bin/gcc-9 -fsanitize=thread  CMakeFiles/cmTC_613bf.dir/testCCompiler.c.o -o cmTC_613bf
    /usr/bin/ld: cannot find libtsan_preinit.o: No such file or directory
    collect2: error: ld returned 1 exit status
    make[1]: *** [CMakeFiles/cmTC_613bf.dir/build.make:99: cmTC_613bf] Error 1
    make[1]: Leaving directory '/home/travis/build/nats-io/nats.c/build/CMakeFiles/CMakeTmp'
    make: *** [Makefile:127: cmTC_613bf/fast] Error 2

From some searches, it seems it is a Ubuntu bug that has not been yet fixed. So disable run for now: https://bugs.launchpad.net/ubuntu/+source/gcc-9/+bug/2029910

Signed-off-by: Ivan Kozlovic ivan@synadia.com

[kozlovic]

@levb If you get a chance tomorrow (01/16/2024), could you review this one? Without this fix, all branch/PRs get a failure due to an Ubuntu bug with the sanitize thread.