Circumvent GDPR redirect on Tumblr feeds by faking a different user agent

Because of Tumblr's borken GDPR efforts it was not possible to subscribe to podcasts hosted as a Tumblr blog (e.g. http://goldentapes.tumblr.com/rss). When accessing such a feed, the feed parser would be redirected to a GDPR consent form instead, unless a magic cookie is set.

Several other feed parsers experienced similar problems and tried to solve it by either automatically POST'ing the consent form to get the magic cookie or by just faking the user agent and pretend to be Googlebot.

I went with the second, much simpler, solution here and hacked a user agent change for tumblr feeds into feedparser.py.

So far I only tested it in the Sailfish SDK Emulator where I was successfully able to subscribe to the Airtime Radio Podcast feed which previously failed with an endless spinning loading indicator.