Bug 36922: Patron attributes - update hint text for "Is a date"

Bug 36922: Patron attributes - update hint text for "Is a date"

The date field for patron attributes is now repeatable (enhancement made
in Koha 24.05 with bug 32610). This updates the hint text to reflect
the change.

Test plan:
1. Go to add a patron attribute (Administration > Patrons and
   circulation > Patron attribute types > + New patron attribute type )
2. Note that the hint for the "Is a date" field says "...Date attributes
   cannot be repeatable or linked to an authorised value category.".
3. Apply the patch.
4. Reload the page.
5. Note that the hint now says "...Date attributes are repeatable,
   but cannot be linked to an authorised value category."
6. Sign off D:

PA amended: 'are repeatable' -> 'can be repeatable'

Signed-off-by: David Nind <david@davidnind.com>
Signed-off-by: Pedro Amorim <pedro.amorim@ptfs-europe.com>
Signed-off-by: Lucas Gass <lucas@bywatersolutions.com>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>