Bug: Downloads RSS feed doesnt fully validate

[JacobCoffee]

Although it doesn't validate:

line 2, column 609: guid must be a full URL, unless isPermaLink attribute is false: 925 (10 occurrences) [help]

... p 2024 01:32:54 +0000</pubDate><guid>925</guid></item><item><title>Pytho ...

https://validator.w3.org/feed/check.cgi?url=https%3A%2F%2Fwww.python.org%2Fdownloads%2Ffeed.rss

https://validator.w3.org/feed/docs/error/InvalidHttpGUID.html says:

guid must be a full URL, unless isPermaLink attribute is false

I think it would be most useful to re-use the URL from link:

<link>https://www.python.org/downloads/release/python-31015/</link>

Originally posted by @hugovk in #1612 (comment)