fix: increase commitlint header-max-length for squashed PR numbers

[brian-smith-tcril]

Description:

The default commitlint header-max-length (from config-conventional) is 100 characters. This is generally not a problem, but in situations where a PR is squashed the default GH web UI behavior appends (#X[...]X) to the commit message header. This can cause commits that have landed to fail commitlint.

This PR just gives us a little wiggle room for those scenarios.

Merge checklist:

• All reviewers approved
• CI build is green
• If adding new checks, followed how_tos/0001-adding-new-checks.rst
• Changelog record added (if needed)
• Documentation updated (not only docstrings) (if needed)
• Commits are squashed