use namespaced version of function

After the upgrade to Puppet 8 we started getting this:

    Error while evaluating a Function Call, deprecation.
    create_ini_settings. This method is deprecated, please use
    inifile::create_ini_settings instead. at
    ["/etc/puppet/code/environments/production/modules/rss2email/manifests/feed.pp",
    52]: (file:
    /etc/puppet/code/environments/production/modules/rss2email/manifests/feed.pp,
    line: 52, column: 3)

refs tpo/tpa/team#42071