How to use the @actions/core.warn function in @actions/core

timeoutScript: Number(get('timeoutScript')),
      delayRequest: Number(get('delayRequest')),
      ignoreRedirects: JSON.parse(get('ignoreRedirects')),
      insecure: JSON.parse(get('insecure')),
      bail: JSON.parse(get('bail')),
      suppressExitCode: JSON.parse(get('suppressExitCode')),
      reporters: get('reporters').split(','),
      reporter: JSON.parse(get('reporter') || null),
      color: get('color'),
      sslClientCert: get('sslClientCert'),
      sslClientKey: get('sslClientKey'),
      sslClientPassphrase: get('sslClientPassphrase')
    }

    if (!options.apiKey) {
      core.warn('No Postman API key provided.')
    }

    if (options.collection.match(idRegex)) {
      options.collection = `${apiBase}/collections/${options.collection}${options.apiKey}`
    }

    if (options.environment.match(idRegex)) {
      options.environment = `${apiBase}/environments/${options.environment}${options.apiKey}`
    }

    if (options.globals) {
      try {
        options.globals = JSON.parse(options.globals)
      } catch (e) {}
    }