text: Title: Failed to use {{key}}={{value}} for nested JSON
  Body: Hi! I wanna write a function to [create a GitHub gist](https://docs.github.com/en/rest/gists/gists?apiVersion=2022-11-28#create-a-gist). This is what I wrote:
  
  ```fish
  function gists__new --description "Create a gist for the authenticated user"
      argparse l/login= p/pat= d/description= P/public f/file= c/content= -- $argv
  
      set login $_flag_login
      set pat $_flag_pat
      set description $_flag_description
  
      set public false
      set --query _flag_public && set public true
  
      set file $_flag_file
      set content $_flag_content
  
      set body "$(jq --null-input '{
              "description": $description,
              "public": $public,
              "files": {
                  ($file): {
                  "content": $content
                  }
              }
          }' \
          --arg description $description \
          --arg public $public \
          --arg file $file \
          --arg content $content)"
  
      https --auth "$login:$pat" POST api.github.com/gists \
          Accept:application/vnd.github+json \
          X-GitHub-Api-Version:$api_version \
          --raw $body
  end
  ```
  
  It works, but requires `jq`. According to [HTTPie docs](https://httpie.io/docs/cli/nested-json) I can get rid of it. I tried to use `{{key}}={{value}}` but failed:
  
  ``` fish
  function gists__new --description "Create a gist for the authenticated user"
      argparse l/login= p/pat= d/description= P/public f/file= c/content= -- $argv
  
      set login $_flag_login
      set pat $_flag_pat
      set description $_flag_description
  
      set public false
      set --query _flag_public && set public true
  
      set file $_flag_file
      set content $_flag_content
  
      https --auth "$login:$pat" POST api.github.com/gists \
          "description=$description" \
          "public=$public" \
          "files[$file][content]=$content" \
          Accept:application/vnd.github+json \
          X-GitHub-Api-Version:$api_version \
  end
  ```
  
  The response I get is:
  
  ```json
  {
      "documentation_url": "https://docs.github.com/rest/gists/gists#create-a-gist",
      "message": "Invalid request.\n\nInvalid input: object is missing required key: files."
  }
  
  ```
  
  What am I doing wrong?