Add support for marking test with multiple GitHub issues

[jladdjr]

Would it make more sense to add the github marker multiple times to a test, list multiple issues within a given marker, both?

Add the github marker multiple times to a test:

• Would allow each issue to key off of a different exception

List multiple issues within a given marker:

• Would be convenient if each issue keyed off of the same exception

Both:

• Would provide the flexibility of using either approach ^