Field label not included in Twig when `markdown: true` is present

[lucasicr]

When including markdown: true (see #233) in a field, the field label no longer appears in {% include "forms/form.html.twig" %}.

Not only the checkbox field is affected, but the text, checkboxes and other fields are too.

Minimal working example

---
form:
    fields:
        personal:
            type: fieldset
            fields:
                email:
                    label: 'email address'
                    type: email
                    validate:
                        required: true
                agreement:
                    type: checkbox
                    markdown: true
                    label: 'I agree to the [terms and conditions](https://mywebsite.com/terms-and-conditions)'
                    validate:
                        required: true
    buttons:
        submit:
            type: submit
            value: Submit
    process:
        email:
            from: no-reply@mywebsite.com
            to: '{{ form.value.email|e }}'
            body: '{% include ''forms/data.html.twig'' %}'
---

Email response:

email: joe@gmail.com
: GRAV.YES

Expected response:

email: joe@gmail.com
I agree to the terms and conditions: GRAV.YES