Fix warning in test_strunescape

Fix warning in test_strunescape

src/utils/common/common_test.c:254:3: warning: ‘strncpy’ output truncated before terminating nul copying 16 bytes from a string of the same length [-Wstringop-truncation]
  254 |   strncpy(buffer, "\\tbackslash end\\", sizeof(buffer));
      |   ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  CCLD     test_common

(cherry picked from commit 5bcc3a10cbae9d94ccb10a62218ab26433bbaa67)
(cherry picked from commit 7109b8a27f2d82fbf8c1ae9d58ab6cffbaec9339)