Ignore Seperator when calculating length of choices in select

[weiduhuo]

What is the problem that this PR addresses?

Ignore Seperator when calculating length of choices in select so that we can make full use of the maximum number of keyboard shortcuts.

How did you solve it?

From

len(choices)

To

sum(1 for c in choices if not isinstance(c, Separator))

Checklist

• I have read the Contributor's Guide.
• I will check that all automated PR checks pass before the PR gets reviewed.

[kiancross]

This looks good, thanks!

For some reason, the CI checks have not run. Can you force-push the commit (might need to do git commit --amend first) to re-trigger the GitHub actions?