Fix assertion for install_allocation_event_hook
Fix assertion for install_allocation_event_hook

The `install_allocation_event_hook` isn't a method on
`Appsignal::Minutely`, but on `Appsignal::Extension`. Must have been a
copy-paste mistake.

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appsignal/appsignal-ruby,appsignal/appsignal-ruby,appsignal/appsignal-ruby,appsignal/appsignal-ruby