Downgrade sidekiq back to 6

Gemfile

@@ -61,7 +61,7 @@ gem 'roo', '~>2.9.0'
 gem 'rsolr', '~> 2.5.0'
 # Use SCSS for stylesheets
 gem 'sass-rails', '~> 6.0.0'
-gem 'sidekiq', '~> 7.3'
+gem 'sidekiq', '~> 6.5'
 gem 'sidekiq-status', '~> 3.0.0'
 # Turbolinks makes navigating your web application faster. Read more: https://github.com/turbolinks/turbolinks
 gem 'turbolinks', '~> 5.2.1'

Gemfile.lock

@@ -829,8 +829,6 @@ GEM
     redic (1.5.3)
       hiredis
     redis (4.5.1)
-    redis-client (0.22.2)
-      connection_pool
     redis-namespace (1.11.0)
       redis (>= 4)
     redlock (1.3.2)
@@ -955,12 +953,10 @@ GEM
       sxp (~> 1.1)
     shoulda-matchers (5.3.0)
       activesupport (>= 5.2.0)
-    sidekiq (7.3.2)
-      concurrent-ruby (< 2)
-      connection_pool (>= 2.3.0)
-      logger
-      rack (>= 2.2.4)
-      redis-client (>= 0.22.2)
+    sidekiq (6.5.12)
+      connection_pool (>= 2.2.5, < 3)
+      rack (~> 2.0)
+      redis (>= 4.5.0, < 5)
     sidekiq-status (3.0.3)
       chronic_duration
       sidekiq (>= 6.0, < 8)
@@ -1147,7 +1143,7 @@ DEPENDENCIES
   sass-rails (~> 6.0.0)
   selenium-webdriver (~> 4.8)
   shoulda-matchers (~> 5.3.0)
-  sidekiq (~> 7.3)
+  sidekiq (~> 6.5)
   sidekiq-status (~> 3.0.0)
   simplecov
   solr_wrapper (~> 4.0.2)