AJAX submission returns invalid JSON

When submitting a form using AJAX (via axios in my case), the JSON response has the action name appended to it, which makes it so that the JSON cannot be parsed (`SyntaxError: JSON.parse: unexpected non-whitespace character after JSON data at line 2 column 1 of the JSON data`).

I am loading the form on the site using `{% include "forms/form.html.twig" with { form: forms('kontakt-ajax') } %}`.

Frontmatter with the form:
```yaml
---
title: Formulár
routable: true
cache_enable: false
visible: false
form:
name: kontakt-ajax
template: form-messages
action: ine/formular
refresh_prevention: true
classes: 'contact-form transition-all transition-100 overflow-hidden'
fields:
# Here is a list of all fields
buttons:
submit:
type: submit
classes: 'px-4 py-2 rounded font-display text-primary-700 bg-primary-200 hover:bg-gray-900 hover:text-gray-200 transition-all transition-250 cursor-pointer w-40'
outerclasses: my-4
value: 'Odoslať správu'
process:
message: 'Ďakujeme, že ste nám napísali! Pokúsime sa Vám odpovedať čo najskôr.'
email:
subject: '{{form.value.category|e}} - {{ form.value.subject|e }} (Kontaktný formulár)'
body: '{% include "forms/data.html.twig" %}'
from: '{{ form.value.email }}'
---
```

JS used for sending the request:
```js
axios({
method: form.method,
url: '/ine/formular.json',
data: {
'name': form.name.value,
'email': form.email.value,
'category': form.category.value,
'subject': form.subject.value,
'message': form.message.value,
'gdpr': form['gdpr-'].value,
'__form-name__': 'kontakt-ajax',
'__unique_form_id__': form.__unique_form_id__.value,
'form-nonce': form['form-nonce'].value
},
headers: {
'Accept': 'application/json',
'Content-Type': 'application/json',
'X-Requested-With': 'XMLHttpRequest'
}
}).then(response => {
console.log(response);
form.style.maxHeight = `${form.scrollHeight}px`;
// Create message
if (response.data.status === 'success') {
// Style message and add content
text.textContent = response.data.message;
text.classList.add('bg-green-200', 'border-green-500', 'border-l-4', 'py-2', 'px-4', 'my-4');
} else {
switch (response.data.message) {
case 'PLUGIN_FORM.FORM_ALREADY_SUBMITTED':
text.textContent = 'Tento formulár ste možno už odoslali. Ak ho chcete skúsiť znovu odoslať, obnovte prosím stránku.';
break;
default:
text.textContent = 'Nastala nejaká chyba, skúste obnoviť stránku.';
}
text.classList.add('bg-red-200', 'border-red-500', 'border-l-4', 'py-2', 'px-4', 'my-4');
}
}).catch(error => {
console.error(error);
})
```

The returned data:
```json
{"status":"success","message":"\u010eakujeme, \u017ee ste n\u00e1m nap\u00edsali! Pok\u00fasime sa V\u00e1m odpoveda\u0165 \u010do najsk\u00f4r."}
ine/formular
```

I managed to hack around it by using `JSON.parse(response.data.split("\n")[0]);`, but that is less than ideal.

Start by reproducing the AJAX request to /ine/formular.json using the supplied form configuration and request headers. Inspect the form response path that handles the JSON response and compare it with the returned data shown in the issue. Done means the endpoint returns parseable JSON without the appended action name.

Written by the indexing model from the issue text.