Sticky Posts reappearing after Infinite Scroll is triggered

#### Steps to reproduce the issue

1. Use a theme that supports IS like Baskerville 2 or Dyad 2
2. Mark as sticky a post that will be loaded only after Infinite Scroll is triggered
3. Check the site

#### What I expected
To see the sticky post at the top and that's it.

#### What happened instead
I see the sticky post at the top but the post is once again loaded once Infinite Scroll is fired.

At the top, before IS:

Once IS is triggered:

#### Context
User report: 3547347-hc

Reproduce the issue with a theme that supports Infinite Scroll, such as Baskerville 2 or Dyad 2, using the listed sticky-post steps. Trace the Infinite Scroll request and post rendering behavior; done means the sticky post appears at the top only once after Infinite Scroll loads more content.

Written by the indexing model from the issue text.