If you add a Search block into a Navigation block, the resultant markup is incorrect. The Search block should be rendered inside a <li>.

Steps to reproduce:

1. Create a new post
2. Insert a Navigation block
3. Insert a Search block into the Navigation block
4. Preview the post and inspect the markup

Expected result:

The <form> should be inside a <li>.

Actual result:

The <form> is inside the <ul>.