gh-130607: Extend and cleanup IPv6 tests

[bazhil]

1. Was added two test cases for IPv6 with part of IPv4.
2. Add space in two lines (896, 897) between variable and '='

Hope this work make ipaddress better.

• Issue: Missing IPv6 testcase for for IPv6 with part of IPv4 #130607

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[picnixz]

I would still want an issue for refactoring this but a skip news is fine. The issue should indicate which tests need to be refactored (essentially all those using == + assertTrue/False; we should use better assert methods) and why some need to be extended.

We can however improve even the testsdoing == by using assertEqual. Traceback will be nicer.

[bazhil]

@picnixz create an issue for this pull request #130607

[encukou]

IMO this is an improvement; any refactoring can be done in a separate PR.