6.x mailer markdown loses strikethrough support from 5.x

[brucek2]

• Laravel Version: 6.18.18
• PHP Version: 7.4.6
• Database Driver & Version: n/a

Description:

After upgrading my app from framework 5.7.29 to 6.18.18, I noticed my email templates that included markdown for strike-through no longer rendered as they did before. The strikethrough wrapper ~~ was passed as-is instead of causing strikethrough.

I believe the source of this issue is the switch to commonmark, and the solution would be as easy as including an option to instantiate commonmark using new GithubFlavoredMarkdownConverter() in place of new CommonMarkConverter()

Steps To Reproduce:

1. Create or edit any markdown mail template to include strikethrough text: text
2. Render the mail template

[driesvints]

It's indeed a feature of Github flavored markdown. But as this is more of a feature request I'm moving this to discussions instead. You can attempt a PR if you want.