Fix warning in test_escape_string

Fix warning in test_escape_string

In function ‘test_escape_string’,
    inlined from ‘main’ at src/utils/common/common_test.c:384:3:
src/utils/common/common_test.c:226:5: warning: ‘strncpy’ specified bound 16 equals destination size [-Wstringop-truncation]
  226 |     strncpy(buffer, cases[i].str, sizeof(buffer));
      |     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~