Multi-part form doesn't support variable values

[williamscs]

I have checked the following:

• I use the newest version of bruno.
• I've searched existing issues and found nothing related to my issue.

Describe the bug

It looks like URL-encoded forms and JSON bodies support sending the value of a variable. When I use multi-part, however, it looks like it just sends the string literally (e.g. "{{variable}}" instead of rendering as "should_have_value")

.bru file to reproduce the bug

meta {
  name: Test Variable
  type: http
  seq: 3
}

post {
  url: https://echo.free.beeceptor.com/
  body: multipartForm
  auth: none
}

body:json {
  {
    "value": "{{variable}}"
  }
}

body:form-urlencoded {
  variable: {{variable}}
}

body:multipart-form {
  variable: {{variable}}
}

vars {
  variable: should_have_value
}

Screenshots/Live demo link

[Its-treason]

Duplicate of #352 I already opened a PR for this #1217