tst-resolv-invalid-cname.c: Explicitly cast 192 and 168 to char

tst-resolv-invalid-cname.c: Explicitly cast 192 and 168 to char

Explicitly cast 192 and 168 to char to silence Clang error:

tst-resolv-invalid-cname.c:313:17: error: implicit conversion from 'int' to 'char' changes value from 192 to -64 [-Werror,-Wconstant-conversion]
  313 |       addr[0] = 192;
      |               ~ ^~~
tst-resolv-invalid-cname.c:314:17: error: implicit conversion from 'int' to 'char' changes value from 168 to -88 [-Werror,-Wconstant-conversion]
  314 |       addr[1] = 168;
      |               ~ ^~~

Signed-off-by: H.J. Lu <hjl.tools@gmail.com>
Reviewed-by: Sam James <sam@gentoo.org>