[pre-commit.ci] pre-commit autoupdate

[pre-commit-ci]

updates:

• github.com/pycqa/isort: 8.0.1 → 9.0.0a3

[pp-mo]

NOTE: as for similar on ugrid-checks repo, this pre-commit update PR looks inappropriate,
in that it is trying to upgrade isort to an alpha release -- which seems like a mistake.

On the other hand, this is showing that other things have drifted, with 13 failures in tests/integration/test_iris_xarray_roundtrips.py::test_roundtrip_ixi.

Not yet certain whether it is iris or xarray which has changed, but note that in these tests :

• iris is 3.15.0
• xarray is 2026.4.0

Whereas in latest known-good main commit tests, have :

• iris is 3.14.1
• xarray is 2026.2.0

This rather highlights the need to do either regular dependency checking, or lockfiles,
-- or maybe just dependabot, but that didn't catch this ??