fix for _oradb_tzupgrade_candidate_pdbs fact

[talek]

When upgrading timezone for a CDB database it fails with:

TASK [opitzconsulting.ansible_oracle.oradb_tzupgrade : oradb_tzupgrade | Show facts for pdbs_info] ***                                                                                             
Wednesday 23 October 2024  22:15:43 +0200 (0:00:00.055)       0:03:57.589 *****                                                                                                                    
fatal: [mol-oracle-pdvmoras99-snapcdb]: FAILED! => {"msg": "The task includes an option with an undefined variable. The error was: '_oradb_tzupgrade_candidate_pdbs' is undefined. '_oradb_tzupgrade
_candidate_pdbs' is undefined\n\nThe error appears to be in '/home/devopsadm/.ansible/collections/ansible_collections/opitzconsulting/ansible_oracle/roles/oradb_tzupgrade/tasks/cdb.yml': line 40, 
column 3, but may\nbe elsewhere in the file depending on the exact syntax problem.\n\nThe offending line appears to be:\n\n\n- name: oradb_tzupgrade | Show facts for pdbs_info\n  ^ here\n"}