Add new intgration test scenario 029

```
  Error:
    × Main thread panicked.
    ├─▶ at crates/lang/src/uplc.rs:2395:56
    ╰─▶ called `Result::unwrap()` on an `Err` value: FreeUnique(Name { text: "test_insert", unique:
        Unique(1) })
  ```

examples/acceptance_tests/029/aiken.toml

@@ -0,0 +1,2 @@
+name = "acceptance_test_029"
+version = "0.0.0"

examples/acceptance_tests/029/lib/test.ak

@@ -0,0 +1,69 @@
+pub opaque type AssocList<key, value> {
+  inner: List<#(key, value)>,
+}
+
+pub fn new() -> AssocList<key, value> {
+  AssocList { inner: [] }
+}
+
+pub fn from_list(xs: List<#(key, value)>) -> AssocList<key, value> {
+  AssocList { inner: do_from_list(xs) }
+}
+
+fn do_from_list(xs: List<#(key, value)>) -> List<#(key, value)> {
+  when xs is {
+    [] -> []
+    [#(k, v), ..rest] -> do_insert(do_from_list(rest), k, v)
+  }
+}
+
+pub fn insert(
+  in m: AssocList<key, value>,
+  key k: key,
+  value v: value,
+) -> AssocList<key, value> {
+  AssocList { inner: do_insert(m.inner, k, v) }
+}
+
+fn do_insert(
+  elems: List<#(key, value)>,
+  k: key,
+  v: value,
+) -> List<#(key, value)> {
+  when elems is {
+    [] -> [#(k, v)]
+    [#(k2, v2), ..rest] ->
+      if k == k2 {
+        [#(k, v), ..rest]
+      } else {
+        [#(k2, v2), ..do_insert(rest, k, v)]
+      }
+  }
+}
+
+pub fn union(
+  left left: AssocList<key, value>,
+  right right: AssocList<key, value>,
+) -> AssocList<key, value> {
+  AssocList { inner: do_union(left.inner, right.inner) }
+}
+
+fn do_union(
+  left: List<#(key, value)>,
+  right: List<#(key, value)>,
+) -> List<#(key, value)> {
+  when left is {
+    [] -> right
+    [#(k, v), ..rest] -> do_union(rest, do_insert(right, k, v))
+  }
+}
+
+fn fixture_1() {
+  new()
+  |> insert("foo", 42)
+  |> insert("bar", 14)
+}
+
+test union_1() {
+  union(fixture_1(), new()) == fixture_1()
+}