FIX: log for CleanUpTags job (#23964)

In previous [PR](https://github.com/discourse/discourse/pull/23864) we introduced setting to automatically delete unused tags. This action should be logged.

app/jobs/scheduled/clean_up_tags.rb

@@ -8,7 +8,14 @@ module Jobs
 
     def execute(args)
       return unless SiteSetting.automatically_clean_unused_tags
-      Tag.unused.where("tags.created_at < ?", GRACE_PERIOD_MINUTES.minutes.ago).destroy_all
+      Tag.transaction do
+        tags = Tag.unused.where("tags.created_at < ?", GRACE_PERIOD_MINUTES.minutes.ago)
+        StaffActionLogger.new(Discourse.system_user).log_custom(
+          "deleted_unused_tags",
+          tags: tags.pluck(:name),
+        )
+        tags.destroy_all
+      end
     end
   end
 end

spec/jobs/clean_up_tags_spec.rb

@@ -43,6 +43,16 @@ describe Jobs::CleanUpTags do
       created_at: 10.minutes.ago,
     )
   end
+  fab!(:unused_tag_2) do
+    Fabricate(
+      :tag,
+      name: "unused2",
+      staff_topic_count: 0,
+      public_topic_count: 0,
+      pm_topic_count: 0,
+      created_at: 10.minutes.ago,
+    )
+  end
 
   fab!(:tag_in_group) do
     Fabricate(
@@ -57,8 +67,17 @@ describe Jobs::CleanUpTags do
 
   it "deletes unused tags" do
     SiteSetting.automatically_clean_unused_tags = true
-    expect { job.execute({}) }.to change { Tag.count }.by(-1)
+    expect { job.execute({}) }.to change { Tag.count }.by(-2)
     expect { unused_tag.reload }.to raise_error(ActiveRecord::RecordNotFound)
+    expect { unused_tag_2.reload }.to raise_error(ActiveRecord::RecordNotFound)
+  end
+
+  it "logs action" do
+    SiteSetting.automatically_clean_unused_tags = true
+    expect { job.execute({}) }.to change { UserHistory.count }.by(1)
+    log = UserHistory.last
+    expect(log.acting_user_id).to eq(-1)
+    expect(log.details).to eq('tags: ["unused1", "unused2"]')
   end
 
   it "does nothing when site setting is disabled by default" do