set correct "type" of PubSubModerationActionChannelTerms

[Dschogo]

Pull request summary

Sets a correct/more descriptive "type" of PubSubModerationActionChannelTerms (from "channel_terms_action" to "add_blocked_term"/"delete_blocked_term")

Checklist

• [x] If code changes were made then they have been tested.
  • [ ] I have updated the documentation to reflect the changes.
  • [x] I have updated the changelog with a quick recap of my changes.
• [x] 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, ...)