Steps to reproduce the issue

Try to setup the credential based login, configure your Github account to use a password with a "#" somewhere in the string. Fetch the list of issues.

Expected result

Issuelist is being fetched.

Actual result

You'll get a connection error.

Additional comments

Add the first glance it looks like the issue is being caused by the lack of encoding for the # character while setting up the connection:
https://github.com/joomla-extensions/patchtester/blob/master/administrator/components/com_patchtester/PatchTester/GitHub/GitHub.php#L88

This leads to a URL like this being used for the connection:

user:pass#word@github.com

The url gets truncated after the #, because that's used for html anchors.

A simple

$password = str_replace('#', '%23', $password);

Should fix it, for both, username and password