It's available for download from the webpage, but not on GitHub. https://www.renpy.org/release/8.5.0

It would be great to have it also here for completeness sake. In case the webpage version went down and someone needed that particular version a few years down the line, it might be very difficult to compile it due to various Python toolings going outdated and/or gone from pip. (And having access to specific outdated versions is very precious when you're trying to gracefully upgrade your game from a very old version to the newest one, while fixing what breaks in-between, going changelog by changelog.)