Update tests to reflect github's new path to raw content

The dynamic sidebar tests use macros, which are located on github via raw
URLs. When they changed their path, it didn't cause any failures while also
slowing down the tests.

I updated the tests to use the new paths and also added a check to verify that
macro content was actually loaded. Both should cause a more recognizable
failure if github makes similar edits.

The impact is that all the guides need to be updated to reflect the new paths.