cmd/cue/cmd: add test for edge case

This was exposed during the work done on
reducing the depth of the closeContext graph.

Signed-off-by: Marcel van Lohuizen <[email protected]>
Change-Id: Ia3ee2d2aa2ec1142704def120c3efe354c55c7e2
Reviewed-on: https://review.gerrithub.io/c/cue-lang/cue/+/1209213
TryBot-Result: CUEcueckoo <[email protected]>
Reviewed-by: Matthew Sackman <[email protected]>

Author: mpvl

cmd/cue/cmd/testdata/script/vet_matchn.txtar

@@ -0,0 +1,32 @@
+# With the old evaluator.
+env CUE_EXPERIMENT=evalv3=0
+exec cue vet -c schema.cue data.json
+
+# With the new evaluator.
+env CUE_EXPERIMENT=evalv3=1
+env CUE_DEBUG=openinline=0
+! exec cue vet -c schema.cue data.json #TODO Fix
+
+-- data.json --
+{
+    "step": {
+        "run": "echo foo"
+    }
+}
+-- schema.cue --
+package githubactions
+
+#Workflow
+
+#Workflow: {
+    step!: matchN(1, [{
+        "uses"!: _
+        ...
+    }, {
+        "run"!: _
+        ...
+    }]) & close({
+        "uses"?: string
+        "run"?:  string
+    })
+}