Don't rely on the removed "role=row" and "role=columnheader" attributes

[gino0631]

The datatable styling relies on "role=row" and "role=columnheader" attributes, e.g.:

admin-theme/src/main/resources/less/primefaces-admin/components/datatable.less

Line 86 in f857cb4

th[role="columnheader"].ui-state-default {

Unfortunately, these attributes were removed in PrimeFaces 12 (primefaces/primefaces#9261), so the corresponding CSS properties no longer get applied.