shared examples `two_factor_authenticatable` failed when set `otp_allowed_drift` to 5

[jsice]

some tests might fail if the otp_allowed_drift is too low

it 'does not validate an OTP above the allowed drift' do
  otp = ROTP::TOTP.new(otp_secret).at(Time.now + subject.class.otp_allowed_drift * 2)
  expect(subject.validate_and_consume_otp!(otp)).to be false
end

it 'does not validate an OTP below the allowed drift' do
  otp = ROTP::TOTP.new(otp_secret).at(Time.now - subject.class.otp_allowed_drift * 2)
  expect(subject.validate_and_consume_otp!(otp)).to be false
end

An OTP is valid for INTERVAL + otp_allowed_drift * 2 seconds but these test cases didn't include the interval so if otp_allowed_drift is less than the interval, the tests may possibly fail