Silence snprintf truncation warnings in printf_test examples

Silence snprintf truncation warnings in printf_test examples

Building share/examples/tests with clang 18 results in a few warnings
like:

  share/examples/tests/tests/plain/printf_test.c:67:6: error: 'snprintf' will always be truncated; specified size is 10, but format string expands to at least 17 [-Werror,-Wformat-truncation]
     67 |         if (snprintf(buffer, sizeof(buffer), "0123456789abcdef") != 16)
        |             ^

Since these tests are meant as an example of testing snprintf overflow,
suppress the warnings.

MFC after:	3 days