Downgrade sidekiq to latest 6.x version

Sidekiq 7 requires redis 6.2+, which isn't available in a lot of distros
yet :( So lets wait with this for a while.

This partially reverts commit a59505574a.

Gemfile

@@ -42,8 +42,8 @@ gem "simple_captcha2", "0.5.0", require: "simple_captcha"
 
 # Background processing
 
-gem "redis-client", "0.14.1"
-gem "sidekiq", "7.1.2"
+gem "redis", "4.8.1"
+gem "sidekiq", "6.5.9"
 
 # Scheduled processing
 

Gemfile.lock

@@ -591,8 +591,7 @@ GEM
     rb-inotify (0.10.1)
       ffi (~> 1.0)
     redcarpet (3.6.0)
-    redis-client (0.14.1)
-      connection_pool
+    redis (4.8.1)
     regexp_parser (2.8.1)
     request_store (1.5.1)
       rack (>= 1.4)
@@ -668,11 +667,10 @@ GEM
     secure_headers (6.5.0)
     shoulda-matchers (5.3.0)
       activesupport (>= 5.2.0)
-    sidekiq (7.1.2)
-      concurrent-ruby (< 2)
-      connection_pool (>= 2.3.0)
-      rack (>= 2.2.4)
-      redis-client (>= 0.14.0)
+    sidekiq (6.5.9)
+      connection_pool (>= 2.2.5, < 3)
+      rack (~> 2.0)
+      redis (>= 4.5.0, < 5)
     sidekiq-cron (1.10.1)
       fugit (~> 1.8)
       globalid (>= 1.0.1)
@@ -868,7 +866,7 @@ DEPENDENCIES
   rails-i18n (= 7.0.7)
   rails-timeago (= 2.20.0)
   redcarpet (= 3.6.0)
-  redis-client (= 0.14.1)
+  redis (= 4.8.1)
   responders (= 3.1.0)
   rqrcode (= 2.2.0)
   rspec-json_expectations (~> 2.1)
@@ -880,7 +878,7 @@ DEPENDENCIES
   sassc-rails (= 2.1.2)
   secure_headers (= 6.5.0)
   shoulda-matchers (= 5.3.0)
-  sidekiq (= 7.1.2)
+  sidekiq (= 6.5.9)
   sidekiq-cron (= 1.10.1)
   simple_captcha2 (= 0.5.0)
   simplecov (= 0.22.0)

app/workers/archive_base.rb

@@ -31,7 +31,7 @@ module Workers
         !(Process.pid.to_s == process_id.split(":")[1] && Thread.current.object_id.to_s(36) == thread_id) &&
           ArchiveBase.subclasses.map(&:to_s).include?(work["payload"]["class"])
       end
-    rescue RedisClient::CannotConnectError
+    rescue Redis::CannotConnectError
       # If code gets to this point and there is no Redis conenction, we're
       # running in a Test environment and have not mocked Sidekiq::Workers, so
       # we're not testing the concurrency-limiting behavior.

script/server

@@ -128,8 +128,7 @@ if [ -n "$redis_url" ]
 then
   redis_param="url: '$redis_url'"
 fi
-echo $redis_param
-if [ "$(bin/bundle exec ruby -e "require 'redis-client'; puts RedisClient.config($redis_param).new_client.call('PING')" 2> /dev/null | grep -vE "is not writable|as your home directory temporarily" )" != "PONG" ]
+if [ "$(bin/bundle exec ruby -e "require 'redis'; puts Redis.new($redis_param).ping" 2> /dev/null | grep -vE "is not writable|as your home directory temporarily" )" != "PONG" ]
 then
   fatal "Can't connect to redis. Please check if it's running and if environment.redis is configured correctly in $CONFIG_FILE."
 fi