Add new acceptance test scenario: expect unary constructors.

```
  Error:
    × Main thread panicked.
    ├─▶ at crates/aiken-lang/src/gen_uplc.rs:1852:33
    ╰─▶ called `Option::unwrap()` on a `None` value
  ```

examples/acceptance_tests/080/lib/tests.ak

@@ -0,0 +1,9 @@
+test foo() {
+  let bar =
+    Void
+
+  expect Void =
+    bar
+
+  True
+}