[issue2551355] Use redbot.org to test https responses

New submission from John Rouillard:

redbot.org acts like lint for http headers. It identified an issue where Last-Modified header
was returning a date with a timezone of -0000. It should have been GMT to match HTTP spec.

Fixed this in changeset:   8018:67922fd17454.

However it is also finding issues with Vary header where Accept-Encoding is not always
added. In cases where encoding is used (gzip, br) the Accept-Encoding value is added.
However when no encoding is used, the Accept-Encoding value is not added. It should be
present to allow the cache to uniquely id the unencoded case according to redbot.

It also reports that requests for a resource done with If-None-Match If-Modified-Since
headers return the full file contents rather than returning an empty body with a 304 not
modified header. I need to debug this case because it might be my caching proxy showing
the issue and not the roundup-server.

Check for other issues as well by hitting different endpoints.

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components: API, Test, Web interface
messages: 8086
nosy: rouilj
severity: normal
status: new
title: Use redbot.org to test https responses
type: behavior

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<https://issues.roundup-tracker.org/issue2551355>
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