Bump sidekiq from 7.2.4 to 7.3.9 in /backend

Bumps [sidekiq](https://github.com/sidekiq/sidekiq) from 7.2.4 to 7.3.9.
- [Changelog](https://github.com/sidekiq/sidekiq/blob/main/Changes.md)
- [Commits](sidekiq/sidekiq@v7.2.4...v7.3.9)

---
updated-dependencies:
- dependency-name: sidekiq
  dependency-version: 7.3.9
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

backend/Gemfile

@@ -32,7 +32,7 @@ gem "omniauth-facebook", "~> 3.0"
 gem "colored"
 
 # Background jobs
-gem "sidekiq", "~> 7.2"
+gem "sidekiq", "~> 7.3"
 
 # Structured seed data
 gem "seedbank"

backend/Gemfile.lock

@@ -127,7 +127,7 @@ GEM
       descendants_tracker (~> 0.0.1)
     colored (1.2)
     concurrent-ruby (1.3.5)
-    connection_pool (2.5.4)
+    connection_pool (2.5.5)
     countries (4.0.1)
       i18n_data (~> 0.13.0)
       sixarm_ruby_unaccent (~> 1.1)
@@ -381,7 +381,7 @@ GEM
     rake (13.2.1)
     rdoc (6.7.0)
       psych (>= 4.0.0)
-    redis-client (0.21.1)
+    redis-client (0.26.1)
       connection_pool
     regexp_parser (2.9.0)
     reline (0.5.9)
@@ -433,11 +433,12 @@ GEM
       rake (>= 10.0)
     shoulda-matchers (6.2.0)
       activesupport (>= 5.2.0)
-    sidekiq (7.2.4)
-      concurrent-ruby (< 2)
+    sidekiq (7.3.9)
+      base64
       connection_pool (>= 2.3.0)
+      logger
       rack (>= 2.2.4)
-      redis-client (>= 0.19.0)
+      redis-client (>= 0.22.2)
     simplecov (0.22.0)
       docile (~> 1.1)
       simplecov-html (~> 0.11)
@@ -547,7 +548,7 @@ DEPENDENCIES
   ruby-progressbar
   seedbank
   shoulda-matchers
-  sidekiq (~> 7.2)
+  sidekiq (~> 7.3)
   simplecov
   sprockets-rails
   standardrb