tests: iterator::workdir: fix GCC warning Since GCC 8.1, the compiler performs some bounds checking when copying static data into arrays with a known size. In one test, we print a format string of "%s/sub%02d" into a buffer of 64 bytes. The input buffer for the first "%s" is bounded to at most 63 characters, plus four bytes for the static string "/sub" plus two more bytes for "%02d". Thus, our target buffer needs to be at least 70 bytes in size, including the NUL byte. There seems to be a bug in the analysis, though, because GCC will not account for the limiting "%02" prefix, treating it as requiring the same count of bytes as a "%d". Thus, we end up at 79 bytes that are required to fix the warning. To make it look nicer and less special, we just round the buffer size up to 80 bytes.