The directory opened with `g_dir_open` is never closed, so LeakSanitizer
complains about a memory leaks.
```
Direct leak of 8 byte(s) in 1 object(s) allocated from:
/build/gcc/src/gcc/libsanitizer/asan/asan_malloc_linux.cc:86
#1 0x7f2012908ac9 in g_malloc (/usr/lib/libglib-2.0.so.0+0x51ac9)
#2 0x7f2012922aac in g_memdup (/usr/lib/libglib-2.0.so.0+0x6baac)
#3 0x7f20128ed2d5 (/usr/lib/libglib-2.0.so.0+0x362d5)
#4 0x7f20128ed338 in g_dir_open (/usr/lib/libglib-2.0.so.0+0x36338)
../tests/datetime/test-endianess.c:29
#6 0x7f201292a76a (/usr/lib/libglib-2.0.so.0+0x7376a)
#7 0x7f201292a69a (/usr/lib/libglib-2.0.so.0+0x7369a)
(/usr/lib/libglib-2.0.so.0+0x73951)
#9 0x7f201292a972 in g_test_run (/usr/lib/libglib-2.0.so.0+0x73972)
#10 0x560ad630cbff in main ../tests/datetime/test-endianess.c:66
```
