New post notifications sent to subscribers for categories they aren't subscribed to when using Newsletter Categories

### Impacted plugin

Jetpack

### Quick summary

When using Newsletter Categories and selecting a single category for users to subscribe to, subscribers still receive new post notifications for any new post created on the site, regardless of the category. It's unknown if this affects only when setting a single category or not, but only a single category was tested as that is what user had setup in this interaction: 7686351-zd-a8c

A workaround is to specifically set the newsletter setting on a post to [Post only](https://wordpress.com/support/subscriptions-and-newsletters/#do-not-send-an-email-for-a-post) on categories you don't want emails sent out for, but this is tedious and an extra step.

### Steps to reproduce

1. Enable Newsletter Categories under Settings > Newsletters and select a single category
2. Add a Subscribe Block somewhere on the site.
3. View the site and submit your email address in the form to subscribe and confirm subscription.
4. [View subscription](https://wordpress.com/read/subscriptions) and see you are subscribed to the category
5. Create a new post that is NOT in the newsletter category and publish it
6. Check your email and see you received a new post notification

### A clear and concise description of what you expected to happen.

Subscribers should only receive emails for new post notifications in categories they are subscribed to as the feature states: _Newsletter categories allow visitors to subscribe only to specific topics. When enabled, only posts published under the categories selected below will be emailed to your subscribers._

### What actually happened

Users receive emails for new post notifications regardless of the category they are subscribed to.

### Impact

Most (> 50%)

### Available workarounds?

Yes, easy to implement

### Platform (Simple and/or Atomic)

Atomic

### Logs or notes

Tested and reproducible on an AT test site only. Simple sites not tested yet.

Start by reproducing the issue through Settings > Newsletters, the Subscribe Block, and the subscription view described in the steps. Trace how Newsletter Categories are used when publishing a post and sending new post notifications; done means subscribers receive notifications only for posts in their selected categories, including on Atomic sites.

Written by the indexing model from the issue text.