tests: close opened directory

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
```

1 files changed, 1 insertions, 1 deletions

diff --git a/tests/datetime/test-endianess.c b/tests/datetime/test-endianess.c
index 06b26131b..9cb92007a 100644
--- a/tests/datetime/test-endianess.c
+++ b/tests/datetime/test-endianess.c
@@ -23,7 +23,7 @@ print_endianess (const char *lang)
 static void
 test_endianess (void)
 {
-	GDir *dir;
+	g_autoptr(GDir) dir = NULL;
 	const char *name;
 
 	dir = g_dir_open ("/usr/share/i18n/locales/", 0, NULL);