CI: Add a spellchecker to pre-commit

[leofang]

Isn't there linters that we can run in CI to catch typos like that?

I don't think we have a spellchecker added to pre-commit, would be nice to add indeed

Originally posted by @leofang in #1041 (comment)

[rwgk]

FWIW, this has been working fine for pybind11 for a few years already:

https://github.com/pybind/pybind11/blob/4dc33d652478e11a1e9b8ba6558d2fbd04a1bee0/.pre-commit-config.yaml#L111-L119

We had to add a suppressions file when we got started:

https://github.com/pybind/pybind11/blob/4dc33d652478e11a1e9b8ba6558d2fbd04a1bee0/.codespell-ignore-lines

Luckily the maintenance burden for that turned out to be very low. Once the spell checker is established, people tend to avoid variable names etc that would make it necessary to add more suppressions.