test/py: test_stackprotector: Disable for ASAN

The stack protector test intentionally overflows a buffer in order to
corrupt the stack canary so that it can test that the corruption is
detected as expected. However, this is incompatible with ASAN, which
detects the buffer overflow and interrupts the test, so disable the test
for such configurations.

Signed-off-by: Andrew Scull <ascull@google.com>