Description of problem:
Reporting this in response to https://bugzilla.redhat.com/show_bug.cgi?id=1993917#c124 testing and discussion.

Version-Release number of selected component (if applicable):
Satellite 6.15.0

How reproducible:
Always

Steps to Reproduce:
1. Configure authenticated/un-authenticated https-proxy
2. Import manifest and enable RH repos
3. Configure setting content_default_http_proxy and http_proxy for created https proxy.
4. Update enabled repos to use specific https proxies and try sync.
5. Navigate to Content -> Subscriptions -> Manage Manifest -> Refresh

Actual results:
Repo sync works, but manifest refresh buttion is disabled with message "This is disabled because no connection could be made to the upstream Manifest."

Expected results:
Manifest refresh also works with https-proxies, like http-proxies

Additional info:

DEV Tracker for https://issues.redhat.com/browse/SAT-23103
Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=2263159