limit pagy dependency to < 43

[manuelmeurer]

Description

Pagy v43 is out: https://ddnexus.github.io/pagy/changelog/#version-4300
It has lots of changes that are incompatible with the current implementation in Avo.
This is why I think it makes sense to limit the dependency to < v43 in the gemspec.
Not sure if the entry in Gemfile can then be removed?

Checklist:

• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have added tests that prove my fix is effective or that my feature works

Manual review steps

1. Add Avo to a app that uses pagy v43
2. App won't start due to errors
3. Limit pagy dependency to < v43
4. App starts fine.

[Paul-Bob]

LGTM!

Thank you for the contribution @manuelmeurer!