Fixes #3685 - Zammad UI should silently discard Cache / apply2file errors.

lib/active_support/cache/zammad_file_store.rb

@@ -7,6 +7,9 @@ module ActiveSupport
         # in certain cases, caches are deleted by other thread at same
         # time, just log it
         super
+      rescue Errno::ENOENT => e
+        Rails.logger.debug { "Can't write cache (probably related to high load / https://github.com/zammad/zammad/issues/3685) #{name}: #{e.inspect}" }
+        Rails.logger.debug e
       rescue => e
         Rails.logger.error "Can't write cache #{name}: #{e.inspect}"
         Rails.logger.error e