Merge branch 'master' into glitch-soc/merge-upstream

Conflicts:
- `app/javascript/mastodon/actions/compose.js`:
  Not a “real” conflict, but change too close to a change we made to
  fix the vanilla WebUI locally pushing authored local-only toots in the
  public TL view.

lib/paperclip/media_type_spoof_detector_extensions.rb

@@ -18,7 +18,7 @@ module Paperclip
       @type_from_mime_magic ||= begin
         begin
           File.open(@file.path) do |file|
-            MimeMagic.by_magic(file)&.type
+            MimeMagic.by_magic(file)&.type || ''
           end
         rescue Errno::ENOENT
           ''