Probably the same answer as in 5e (there the test was Arcana+Int, so aspected magicians could also get in trouble)
Since it's an extended test, if your magic is half decent you shouldn't run into problems for a while even on a pure magic roll, but I'm curious what the answer was too.
The difference between 5th and 6th edition is that in 5th edition;
Arcana was a skill that all awakened were allowed to take (and it was also a good idea for everyone to pick if you ever planned on initiating)
...while in 6th edition;
A physical adept is not allowed to have sorcery, enchanting nor conjuring. That pretty much only leave Astral. But unless the physical adept have access to astral perception (which far from all will have since they now leave chargen with a very limited amount of power points) even the Astral skill is out of reach for them.
For now I lean towards what SSDR said;
Just pick whatever your highest skill is and argue that you use your magic through that skill (game mechanic wise this mean physical adepts will probably end up with a dice pool of 6 + Magic, just like regular full magicians and mystic adepts).
