Normalize case and make small changes in the reference implementation for dependency groups resolution

[jonathandung]

raise TypeError("Dependency Groups table is not a dict")

->

raise TypeError("Dependency groups table is not a dict")

dependency_groups_raw = pyproject["dependency-groups"]
dependency_groups = _normalize_group_names(dependency_groups_raw)
print("\n".join(resolve(pyproject["dependency-groups"], sys.argv[1])))

->

dependency_groups_raw = pyproject["dependency-groups"]
dependency_groups = _normalize_group_names(dependency_groups_raw)
print("\n".join(resolve(dependency_groups_raw, sys.argv[1])))

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📚 Documentation preview 📚: https://python-packaging-user-guide--2045.org.readthedocs.build/en/2045/