Fix test: follow ActiveRecord 8.1 behavior

In ActiveRecord 8.1+, replica connections cannot execute lock queries,
so it raises ActiveRecord::ReadOnlyError instead of ActiveRecord::Deadlocked.

Author: ohbarye

spec/activerecord/debug_errors/ext/connection_adapters/abstract_mysql_adapter_spec.rb

@@ -58,11 +58,15 @@ def cause_deadlock(role:)
 
       context "when the user doesn't have the permission to execute 'SHOW ENGINE INNODB STATUS'" do
         it "displays an error message" do
+          # In ActiveRecord 8.1+, replica connections cannot execute lock queries,
+          # so it raises ActiveRecord::ReadOnlyError instead of ActiveRecord::Deadlocked.
+          expected_error = ActiveRecord.version < Gem::Version.new("8.1") ? ActiveRecord::Deadlocked : ActiveRecord::ReadOnlyError
+
           expect {
             ActiveRecord::Base.connected_to(role: :reading) do
               cause_deadlock(role: :reading)
             end
-          }.to raise_error(ActiveRecord::Deadlocked)
+          }.to raise_error(expected_error)
           expect(log.string).to include("Failed to execute")
         end
       end