internal/cuetxtar: report full result for cuetxtar test failures

This makes it easier to see the full string in order to
(for example) paste it into the test data.

Signed-off-by: Roger Peppe <[email protected]>
Change-Id: I2897e7657dd1a7c53d3799c6c2d9eed556c8af5a
Reviewed-on: https://review.gerrithub.io/c/cue-lang/cue/+/1168507
Reviewed-by: Paul Jolly <[email protected]>
TryBot-Result: CUEcueckoo <[email protected]>
Unity-Result: CUE porcuepine <[email protected]>

Author: rogpeppe

internal/cuetxtar/txtar.go

@@ -434,7 +434,9 @@ func (x *TxTarTest) Run(t *testing.T, f func(tc *Test)) {
 
 				t.Errorf("result for %s differs: (-want +got)\n%s",
 					sub.name,
-					cmp.Diff(string(gold.Data), string(result)))
+					cmp.Diff(string(gold.Data), string(result)),
+				)
+				t.Errorf("actual result: %q", result)
 			}
 
 			// Add remaining unrelated files, ignoring files that were already