Add new acceptance test scenario 025

```
  help: ┍━ left ━━━━━━━━┑
        │ (con unit ()) │
        ┕━━━━━━━━━━━━━━━┙

        should be equal to

        ┍━ right ━━━━━━━┑
        │ (con unit ()) │
        ┕━━━━━━━━━━━━━━━┙
  ```

examples/acceptance_tests/025/aiken.toml

@@ -0,0 +1,2 @@
+name = "acceptance_test_025"
+version = "0.0.0"

examples/acceptance_tests/025/lib/test.ak

@@ -0,0 +1,3 @@
+test nil_1() {
+  Nil == Nil
+}