Pin CI to same nightly as test runner - #179

Alright, I think I resolved the breakage. In Tournament, we use vertical lines in the expected output. ~|foo| interpolates a string using the value of foo. Some combination of unitt and Arturo at this particular nightly is seeing "Team |MP| ..." as us wanting to interpolate the value of MP even though we don't have the tilde prefixing the string. This behavior doesn't happen in the REPL which correctly prints Team |MP| .... It also doesn't happen with the same version of unitt on a later nightly so it must be using some functionality inside Arturo that subtly changed in the last couple of months.

I think the easiest solution is to swap out the vertical bar for something similar like ❙ (MEDIUM VERTICAL BAR). I can clarify this situation in the append Glenn already made.