Bug 27857: Fix Pseudonymization.t

Bug 27857: Fix Pseudonymization.t

t/db_dependent/Koha/Pseudonymization.t .. 2/3
    #   Failed test 'Attribute 1 should be retrieved correctly'
    #   at t/db_dependent/Koha/Pseudonymization.t line 198.
    #     Structures begin differing at:
    #          $got->{borrowernumber} = Does not exist
    #     $expected->{borrowernumber} = '58'

    #   Failed test 'Attribute 2 should be retrieved correctly'
    #   at t/db_dependent/Koha/Pseudonymization.t line 204.
    #     Structures begin differing at:
    #          $got->{borrowernumber} = Does not exist
    #     $expected->{borrowernumber} = '58'
    # Looks like you failed 2 tests of 3.
t/db_dependent/Koha/Pseudonymization.t .. 3/3

Highlighted by
  commit 7b40ee22035210e3fbdfe75785d68ca314285409
  Bug 27857: Make Koha::Patron->extended_attributes validate data

Koha::Patron->add_extended_attributes should not modify the $attribute
hashref parameter we passed.

Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>