Describe the bug

When running spectral lint with --format json against a valid OpenAPI document that produces no findings, the output is []No results with a severity of 'warn' or higher found! instead of just []. The informational message is
appended directly to the JSON array, making the output invalid JSON and breaking any tooling that parses stdout.

To Reproduce

1. Given this OpenAPI document valid.yaml:

  openapi: "3.0.3"                                                                                                                                                                                                                  
  info:                                                                                                                                                                                                                             
    title: Test                                                                                                                                                                                                                     
    version: "1.0.0"
    description: Test API
    contact:
      name: test
  paths: {}
  servers:
    - url: https://example.com

2. Run:
   spectral lint valid.yaml --format json --fail-severity warn

3. stdout is:
   []No results with a severity of 'warn' or higher found!

This is not valid JSON.

Expected behavior

When --format json is used, stdout should contain only valid JSON. The informational message No results with a severity of 'warn' or higher found! should either be suppressed, written to stderr, or not appended to the JSON
output. Expected stdout:

  []

Environment:

• Library version: 6.15.0
• OS: Linux