Fix GroupRoleSerializer domain field view_name typo

[gerrod3]

Summary

• Fixed typo in GroupRoleSerializer.domain field: view_name="domain-detail" → view_name="domains-detail", matching the correct URL pattern name used in UserRoleSerializer.
• This caused a NoReverseMatch error (HTTP 500) whenever a group role with a non-null domain was serialized, and also when rendering the browsable API form (which enumerates domain choices).

Test plan

• Added functional test test_group_roles_with_domain that creates a group role with the default domain and verifies it can be listed and the domain href is correct.

Fixes #7095

Made with Cursor

[gerrod3]

This PR is a test of the new claude.md changes here: #7345. Prompts used:

Solve this issue: https://github.com/pulp/pulpcore/pull/7345
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test the fix
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change the test to a functional one
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why did the issue originally happen for browser requests, but not curl?
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so the error should always happen for any group-role with domain? let's update the test to reflect this
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ok lets make a pr

The first prompt solved the problem. The second one wrote a unit test and checked that it passed. The next three were me reviewing the fix and why it worked and getting it to use a functional test. The last one created the changelog entry and commit, then push and created the PR.

Seems we need a lint step in the PR checklist, although that should soon be replaced with the pre-commit lint hook.