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/aiken.lock

@@ -0,0 +1,5 @@
+# This file was generated by Aiken
+# You typically do not need to edit this file
+
+requirements = []
+packages = []

examples/acceptance_tests/058/aiken.toml

@@ -0,0 +1,2 @@
+name = "aiken-lang/acceptance_test_058"
+version = "0.0.0"

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)
+  }
+}