feat: handle single constr when with multiple branches

Add case to acceptance test 40
Add special case for top level single constr in a when.

examples/acceptance_tests/040/lib/tests.ak

@@ -73,3 +73,12 @@ test single_field_expect() {
   expect CreateVoteBatch { id } = redeemer
   id == #""
 }
+
+test single_when() {
+  let redeemer = CreateVoteBatch { id: #"" }
+  let x = when redeemer is {
+    CreateVoteBatch { id } -> id == #""
+    _ -> False
+  }
+  x == True
+}