Links in Headings generate unrendered Markdown in TOC

[sewid]

Version(s) affected: 1.5.7

Description
If a heading contains a link, the TOC shows plain markdown code

How to reproduce
Enabled extensions:

• TableOfContentsExtension
• TableExtension
• SmartPunctExtension
• HeadingPermalinkExtension
• FootnoteExtension

Render this markdown code

This is the site content

## This is a heading

## Another heading

## [Third heading](https://example.com) is a link

Returned TOC is:

This is a heading

Another heading

[Third heading](https://example.com) is a link

Possible Solution

Additional context

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[colinodell]

This has been fixed in 1.5.8