internal/core/adt: update TestX to include language version

Tests otherwise won't run.

Signed-off-by: Marcel van Lohuizen <mpvl@gmail.com>
Change-Id: I89445026010724417b4e1d9e5860b9cf3cb0fcc3
Reviewed-on: https://review.gerrithub.io/c/cue-lang/cue/+/1195896
TryBot-Result: CUEcueckoo <cueckoo@cuelang.org>
Unity-Result: CUE porcuepine <cue.porcuepine@gmail.com>
Reviewed-by: Daniel Martí <mvdan@mvdan.cc>

internal/core/adt/eval_test.go

@@ -239,6 +239,8 @@ func TestX(t *testing.T) {
 -- cue.mod/module.cue --
 module: "mod.test"
 
+language: version: "v0.9.0"
+
 -- in.cue --
 	`