FIX: pending_assigns_reminder reminder leaking total assigned topics count

[Grubba27]

Before this commit, the reminder leaked the total assigned topics count in the title, which is inconsistent with the UI.

In the post raw, it was ensured that it was not being leaked, but the title was still leaking the count.

Also, add specs and update existing ones to ensure the count is not leaked in the title.

How it was looking before(post.raw) from specs:

You currently have [3 pending assignments](http://test.localhost/u/bruce0/activity/assigned).

### Newest
- [This is a test topic 1](/t/this-is-a-test-topic-1/169) - assigned less than 1 minute ago
- [This is a test topic 0](/t/this-is-a-test-topic-0/168) - assigned less than 1 minute ago

it should be 2 pending assignments

Now:

You currently have [2 pending assignments](http://test.localhost/u/bruce0/activity/assigned).

### Newest
- [This is a test topic 1](/t/this-is-a-test-topic-1/174) - assigned less than 1 minute ago
- [This is a test topic 0](/t/this-is-a-test-topic-0/173) - assigned less than 1 minute ago

It is related to 4630dab

[markvanlan]

So good, thank you