cue/testdata: add regression test for issue 1867

All three versions of the reproducer now fail on evalv2 and evalv3
as one would expect.

Closes #1867.

Signed-off-by: Daniel Martí <[email protected]>
Change-Id: Ia3c923a7dd3e57bfb9a577848e40044496e3a8a2
Reviewed-on: https://review.gerrithub.io/c/cue-lang/cue/+/1214572
TryBot-Result: CUEcueckoo <[email protected]>
Unity-Result: CUE porcuepine <[email protected]>
Reviewed-by: Matthew Sackman <[email protected]>

Author: mvdan