Description of problem:
proxy=_none_ is not handled correctly by dnf in RHEL 8 when used instead of empty string as per man page of dnf.conf (For backward compatibility, '_none_' can be used instead of the empty string)

Version-Release number of selected component (if applicable):
dnf-4.7.0-11.el8.noarch

How reproducible:


Steps to Reproduce:
1. Added proxy=_none_ in /etc/dnf/dnf.conf
           # grep proxy /etc/dnf/dnf.conf 
           proxy=_none_

2. Clean cache and repolist
          # dnf repolist -v

Actual results:
Fails with:
Red Hat Enterprise Linux 8 for x86_64 - AppStream (RPMs)                                                                                     0.0  B/s |   0  B     00:00    
Errors during downloading metadata for repository 'rhel-8-for-x86_64-appstream-rpms':
  - Curl error (5): Couldn't resolve proxy name for https://cdn.redhat.com/content/dist/rhel8/8.6/x86_64/appstream/os/repodata/repomd.xml [Could not resolve proxy: _none_]
Error: Failed to download metadata for repo 'rhel-8-for-x86_64-appstream-rpms': Cannot download repomd.xml: Curl error (5): Couldn't resolve proxy name for https://cdn.redhat.com/content/dist/rhel8/8.6/x86_64/appstream/os/repodata/repomd.xml [Could not resolve proxy: _none_]


Expected results:
No error should be observed

Additional info:
With empty string instead of _none_ no error seen 
# grep proxy /etc/dnf/dnf.conf 
proxy=