utils/gems: run bundle clean when install not required

Library/Homebrew/utils/gems.rb

@@ -194,8 +194,18 @@ module Homebrew
           end
           false
         end
-      else
+      elsif system bundle, "clean" # even if we have nothing to install, we may have removed gems
         true
+      else
+        message = <<~EOS
+          failed to run `#{bundle} clean`!
+        EOS
+        if only_warn_on_failure
+          opoo_if_defined message
+        else
+          odie_if_defined message
+        end
+        false
       end
 
       if bundle_installed