tests: kernel: disable one test for qemu_cortex_a9

Currently a test is failing.

```
twister -i -p qemu_cortex_a9 \
  -s tests/kernel/fatal/exception/kernel.common.stack_sentinel
```

Disable those temporarily until a fix is in place.

Signed-off-by: Christopher Friedt <chrisfriedt@gmail.com>
1 file changed