cue/testdata: add regression test for issue 2310

evalv2 incorrectly fails with structural cycle errors,
but evalv3 handles this correctly.

Closes #2310.

Signed-off-by: Daniel Martí <[email protected]>
Change-Id: I7fc75fbd04df4be42b5fe554f0f0cd7d708a3360
Reviewed-on: https://review.gerrithub.io/c/cue-lang/cue/+/1214721
TryBot-Result: CUEcueckoo <[email protected]>
Unity-Result: CUE porcuepine <[email protected]>
Reviewed-by: Matthew Sackman <[email protected]>

Author: mvdan