Fix memory leak for ruby 3.2

[konalegi]

After switching to Ruby 3.2 we started to get a memory leak. I don't have any explanation for why it so, it looks like something significant has changed in ruby 3.2 in terms of sigleton_class.eval.

Ruby 3.2 (without fix) (green line) vs ruby 3.0 (orange line) memory consumption graphs

after the fix has been applied

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