from_email not substituted from filed

I have the following configuration in my form configuration:

```yaml
from_name: name
from_email: email_address
```

I expect `from_name` and `from_email` to be substituted with value from `name` and `email_address` fields defined for the form:

```yaml
fields:
name:
type: text
options:
required: true
label: Name and surname
attr:
placeholder: Place your name here...
constraints: [ NotBlank ]

email_address:
type: email
options:
required: true
label: E-mail address
attr:
placeholder: Your e-mail address
constraints: [ NotBlank, Email ]
```

However, it seems not to happen as on submission I'm receiving 500 error: `An exception has been thrown during the rendering of a template ("Email "email_address" does not comply with addr-spec of RFC 2822.").` It looks that `email_address` is treated as a string literal rather than field name.

```
bolt/core 4.2.2 🧿 Bolt 4 Core
bolt/forms 1.4.7 📦 This Bolt extension can be used to handle forms in your Bolt 4 project.
```