Pin matplotlib to <3.9.0

[IAlibay]

Towards #878

Checklist

• [ ] Added a news entry

Developers certificate of origin

• [x] I certify that this contribution is covered by the MIT License here and the Developer Certificate of Origin at https://developercertificate.org/.

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 92.17%. Comparing base (43eccaa) to head (d5eacc9).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #879 +/- ## ========================================== - Coverage 93.98% 92.17% -1.81% ========================================== Files 134 134 Lines 9790 9790 ========================================== - Hits 9201 9024 -177 - Misses 589 766 +177 ``` | [Flag](https://app.codecov.io/gh/OpenFreeEnergy/openfe/pull/879/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=OpenFreeEnergy) | Coverage Δ | | |---|---|---| | [fast-tests](https://app.codecov.io/gh/OpenFreeEnergy/openfe/pull/879/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=OpenFreeEnergy) | `92.17% <ø> (?)` | | | [slow-tests](https://app.codecov.io/gh/OpenFreeEnergy/openfe/pull/879/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=OpenFreeEnergy) | `?` | | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=OpenFreeEnergy#carryforward-flags-in-the-pull-request-comment) to find out more.

:umbrella: View full report in Codecov by Sentry.
:loudspeaker: Have feedback on the report? Share it here.

[IAlibay]

Superseded by #880