GitHub onebox wrongly adds extra empty lines after each code line in the emails

[dmitry_fedyuk (Dmitrii Fediuk)]

An original code (correct rendering):
https://github.com/magento/magento2/blob/720667e/lib/internal/Magento/Framework/DB/Transaction.php#L49-L60

A email with the code (wrong rendering: extra empty lines are added, the screenshot is taken in the GMail web interface):

[sam (Sam Saffron)]

Are you sure there are empty lines there and its not simply that the CSS is a bit off?

[dmitry_fedyuk (Dmitrii Fediuk)]

The line breaks between the <li> tags are preserved because the code is inside the <pre> tag.
Additionally, each line of code has a bottom padding of 10px:

[dmitry_fedyuk (Dmitrii Fediuk)]

Now it became even worse: the violet background now covers only a part of the code block: