While we wait for the mimemagic fiasco to clear up, you can use this repo to run the version of mimemagic you used to run.
By using an older version of mimemagic you don't need to worry about installing new dependencies. If your deploys are currently stuck, you may find this helpful.
This is GPL code. This is not legal advice, but lots of people on the internet consider the GPL license safe for SaaS products. If that's you, you could use this approach to get your deploys working again while waiting for the mimemagic dependency on Rails to be removed. Do not use this approach if you can't have GPL code in your repo. This is not legal advice. Ask a lawyer if you aren't sure.
To use an older mimemagic:
gem "mimemagic", git: "https://github.com/TandaHQ/mimemagic-but-gpl.git", ref: "40dd02bb6b442535f97c35326c0383bc67146ac4"You can use any ref you like; 40dd02bb6b442535f97c35326c0383bc67146ac4 is the last ref before the licensing changes started. You can verify this in the repo's history.
The only reason this fork exists is in case the https://github.com/mimemagicrb/mimemagic gets yanked or its history rewritten. You may want to consider your own fork.