fix(automod): improve validation for invalid actions

[shiftinv]

Summary

This improves validation in Guild.create_automod_rule and AutoModRule.edit, now raising a proper TypeError for invalid action types in the most common error cases.

ref: https://canary.discord.com/channels/808030843078836254/1093894067135463475

Checklist

• If code changes were made, then they have been tested
  • I have updated the documentation to reflect the changes
  • I have formatted the code properly by running pdm lint
  • I have type-checked the code by running pdm pyright
• This PR fixes an issue
• This PR adds something new (e.g. new method or parameters)
• This PR is a breaking change (e.g. methods or parameters removed/renamed)
• This PR is not a code change (e.g. documentation, README, ...)