set 3-space indentation

For some reason in the issue templates the issue that gets created doesn't like 2-space nesting. It's a little counter-intuitive since the template itself renders without issue. However, the eventual issue that gets created has nesting display issues and is difficult to read.

I'm looking at our markdown guide and I see that the sub-list items are indented with 3 spaces.

This merge request replaces the 2-space nesting with 3-space nesting.

We could also probably add a check to our CI.