Add new acceptance test scenario: 058

Doesn't like var patterns in list pattern-matching

  ```
  Error:
    × Main thread panicked.
    ├─▶ at crates/aiken-lang/src/uplc.rs:770:29
    ╰─▶ internal error: entered unreachable code
  ```

examples/acceptance_tests/058/lib/tests.ak

@@ -0,0 +1,19 @@
+fn whatever(_xs) {
+  True
+}
+
+test foo() {
+  let xs = [1, 2, 3]
+  when xs is {
+    [x] -> x == 1
+    _ -> whatever(xs)
+  }
+}
+
+test bar() {
+  let xs = [1, 2, 3]
+  when xs is {
+    [x] -> x == 1
+    ys -> whatever(ys)
+  }
+}