ipv6 addresses now need to be valid in 3.9+

`test_hosts` has a comment
```
# Invalid, but well-formed, IPv6 addresses shouldn't raise an
# exception because urlparse.urlsplit() doesn't raise an
# exception on invalid IPv6 addresses.
```

This I think is true in 3.8 and below, but not in 3.9 (3.9.21 tested) which now gets
```
ERROR: test_hosts (test_furl.TestFurl)
----------------------------------------------------------------------
Traceback (most recent call last):
File "/home/palfrey/src/furl/tests/test_furl.py", line 1661, in test_hosts
furl.furl('http://[0:0:0:0:0:0:0:1:1:1:1:1:1:1:1:9999999999999]/')
File "/home/palfrey/src/furl/furl/furl.py", line 1381, in __init__
self.load(url) # Raises ValueError on invalid URL.
File "/home/palfrey/src/furl/furl/furl.py", line 1406, in load
tokens = urlsplit(url)
File "/home/palfrey/src/furl/furl/furl.py", line 312, in urlsplit
scheme, netloc, path, query, fragment = urllib.parse.urlsplit(url)
File "/home/palfrey/.local/share/uv/python/cpython-3.9.21-linux-x86_64-gnu/lib/python3.9/urllib/parse.py", line 510, in urlsplit
_check_bracketed_host(bracketed_host)
File "/home/palfrey/.local/share/uv/python/cpython-3.9.21-linux-x86_64-gnu/lib/python3.9/urllib/parse.py", line 453, in _check_bracketed_host
ip = ipaddress.ip_address(hostname) # Throws Value Error if not IPv6 or IPv4
File "/home/palfrey/.local/share/uv/python/cpython-3.9.21-linux-x86_64-gnu/lib/python3.9/ipaddress.py", line 53, in ip_address
raise ValueError(f'{address!r} does not appear to be an IPv4 or IPv6 address')
ValueError: '0:0:0:0:0:0:0:1:1:1:1:1:1:1:1:9999999999999' does not appear to be an IPv4 or IPv6 address
```
which is breaking the tests. Should these dummy addresses be set to something valid now?