Bug 16177: Fix tests for ColumnsSsettings.t

 Bug 16177: Fix tests for ColumnsSsettings.t

This failure has been introduced by
  commit 243b797dd11bc0ac1f475195ab765ffbf2220f8b
    Bug 15285: Update common files

This is because the cannot_be_modified key is not always created by
C4::Utils::DataTables::ColumnsSettings subroutines

Test plan:
  prove t/db_dependent/ColumnsSettings.t
should return green
And you can also test a table where the feature is set and a column
cannot be modified from the admin page.

NOTE: Works as described. I was pondering this potential
      solution when I found it in bugzilla.

Signed-off-by: Mark Tompsett <mtompset@hotmail.com>
Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Brendan A Gallagher <brendan@bywatersolutions.com>