FIX: Allow Symbol objects to be deserialized in PostRevision (#17510)

Followup to ee07f6da7d

config/application.rb

@@ -102,7 +102,7 @@ module Discourse
     config.action_controller.forgery_protection_origin_check = false
     config.active_record.belongs_to_required_by_default = false
     config.active_record.legacy_connection_handling = true
-    config.active_record.yaml_column_permitted_classes = [Hash, HashWithIndifferentAccess, Time]
+    config.active_record.yaml_column_permitted_classes = [Hash, HashWithIndifferentAccess, Time, Symbol]
 
     # we skip it cause we configure it in the initializer
     # the railtie for message_bus would insert it in the

spec/models/post_revision_spec.rb

@@ -23,4 +23,15 @@ describe PostRevision do
       }
     )
   end
+
+  it "can serialize and deserialize symbols" do
+    # Plugins may store symbolized values in this column
+    pr = Fabricate(:post_revision, modifications: { key: :value })
+    pr.reload
+    expect(pr.modifications).to eq(
+      {
+        key: :value
+      }
+    )
+  end
 end