refact: TraceKind -> TracePrint

Co-authored-by: Rebecca Turner <rbt@sent.as>

src/libexpr/primops.cc

@@ -826,7 +826,7 @@ static void prim_addErrorContext(EvalState & state, const PosIdx pos, Value * *
         auto message = state.coerceToString(pos, *args[0], context,
                 "while evaluating the error message passed to builtins.addErrorContext",
                 false, false).toOwned();
-        e.addTrace(nullptr, HintFmt(message), TraceKind::Custom);
+        e.addTrace(nullptr, HintFmt(message), TracePrint::Always);
         throw;
     }
 }