bundle install をしたときに mimemagic に関するエラーが出てきた。

$ bundle install
Your bundle is locked to mimemagic (0.3.5), but that version could not be found in any of the sources listed in your Gemfile. If you haven't changed sources, that means the author of mimemagic (0.3.5) has
removed it. You'll need to update your bundle to a version other than mimemagic (0.3.5) that hasn't been removed in order to install.

少し調べててみると 0.3.6 以下のバージョンが消されているようだった。　

0.4.3 - March 26, 2021 (11.5KB)
0.4.2 - March 25, 2021 (11KB)
0.4.1 - March 25, 2021 (11KB)
0.4.0 - March 24, 2021 (42.5KB) yanked
0.3.10 - March 26, 2021 (12KB)
0.3.9 - March 25, 2021 (11KB)
0.3.8 - March 25, 2021 (11KB)
0.3.7 - March 25, 2021 (11KB)
0.3.6 - March 24, 2021 (407KB) yanked
0.3.5 - May 04, 2020 (401KB) yanked
0.3.4 - January 28, 2020 (401KB) yanked
0.3.3 - December 20, 2018 (394KB) yanked
0.3.2 - August 02, 2016 (358KB) yanked
0.3.1 - January 04, 2016 (345KB) yanked
0.3.0 - March 25, 2015 (347KB) yanked

そこで対象のGemfileをupdate

$ bundle update mimemagic

無事にbundle install できました。