Bug 35602: Fix typo AutoMemberNum

Bug 35602: Fix typo AutoMemberNum

The correct spelling is autoMemberNum.

To test:
* Enable autoMemberNum system preference
* Set cardnumber to mandatory in BorrowerMandatoryField
* Add a new patron account
* Verify correct spelling in hint below cardnumber input field

Signed-off-by: David Nind <david@davidnind.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Katrin Fischer <katrin.fischer@bsz-bw.de>
(cherry picked from commit 78b4fac242f2e4dd940aff0811abccf4aa093b1e)
Signed-off-by: Fridolin Somers <fridolin.somers@biblibre.com>