Subtitle doesn't support HTML

[krispy1298]

Steps required to reproduce the problem

1. Add the following filter to instant_articles_subtitle:

function instant_articles_subtitle($subtitle, $instant_article_post) {
    return '<i>Example</i> Subititle with Italics';
}

2. Find a post and hit update.
3. Check Debug Result

Expected Result

<h2><i>Example</i> Subititle with Italics</h2>

Actual Result

<h2>&lt;i&gt;Example&lt;/i&gt; Subititle with Italics</h2>

Version Info

Please state exact versions, not latest or new.

• Plugin version: 4.2
• WordPress version: 5.3.2
• PHP version: 7.2

Without the above information we are not able to debug the issue and will close it.