The timezone information is allocated with `tz_info_from_location` but
never deallocated.
LeakSanitizer complains about this memory leak.
```
Direct leak of 13568 byte(s) in 424 object(s) allocated from:
/build/gcc/src/gcc/libsanitizer/asan/asan_malloc_linux.cc:95
#1 0x7f63899bab21 in g_malloc0 (/usr/lib/libglib-2.0.so.0+0x51b21)
../tests/datetime/test-timezone-gfx.c:30
#3 0x7f63899dc76a (/usr/lib/libglib-2.0.so.0+0x7376a)
```