Stop using more-itertools

We barely use it; the couple places that do are not really worth the
extra dependency, I think the code is clearer without it.

Also simplifies one (regular) itertools usage.

Also improves a check and an error message in `pytest.raises`.

1 files changed, 1 insertions, 0 deletions

diff --git a/changelog/7587.trivial.rst b/changelog/7587.trivial.rst
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+The dependency on the ``more-itertools`` package has been removed.