Attempt fix to Heroku server rubygems/rubygems#4269

Gemfile.lock

@@ -1,6 +1,6 @@
 GIT
   remote: https://github.com/activeadmin/activeadmin.git
-  revision: 7367d9ec810b5d35ae29a38f10b75df74058e488
+  revision: 65ef4215ce31c8b0393118d1522fd700baf75426
   specs:
     activeadmin (2.11.1)
       arbre (~> 1.2, >= 1.2.1)
@@ -215,6 +215,7 @@ GEM
     method_source (1.0.0)
     mini_magick (4.11.0)
     mini_mime (1.1.2)
+    mini_portile2 (2.8.0)
     minitest (5.15.0)
     multi_json (1.15.0)
     net-imap (0.2.3)
@@ -232,6 +233,9 @@ GEM
       net-protocol
       timeout
     nio4r (2.5.8)
+    nokogiri (1.13.3)
+      mini_portile2 (~> 2.8.0)
+      racc (~> 1.4)
     nokogiri (1.13.3-arm64-darwin)
       racc (~> 1.4)
     nokogiri (1.13.3-x86_64-linux)
@@ -383,6 +387,7 @@ GEM
 
 PLATFORMS
   arm64-darwin-21
+  ruby
   x86_64-linux
 
 DEPENDENCIES