古いDiscourseインストール用のプラグインとテーマのバージョンを固定する（.discourse-compatibility）

[david (David Taylor)]

No. 3.5.0 is considered “higher” than the prerelease version “3.5.0.beta8-dev”.

You can always try out comparisons on a ruby console:

> Gem::Version.new("3.5.0") < Gem::Version.new("3.5.0.beta8-dev")
=> false