Execute ConfirmationValidator validation when _confirmation's value is false

[bogdanvlviv]

In according to our documentation ConfirmationValidator validation shouldn't be executed only if _confirmation's value is nil.

https://github.com/rails/rails/blob/8a2ee3d8c6921ce34e597658e3f2b43b41423d1d/guides/source/active_record_validations.md#confirmation

rails/activemodel/lib/active_model/validations/confirmation.rb

Lines 60 to 62 in 8a2ee3d

	# NOTE: This check is performed only if +password_confirmation+ is not
	# +nil+. To require confirmation, make sure to add a presence check for
	# the confirmation attribute:

[rails-bot]

r? @eileencodes

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