Fix UserDefaultAttrprop::set_enum_labels: overwrite labels instead of append

Yury Matveevrequested to merge
1368-userdefaultattrprop-set_enum_labels-does-append-enum-labels into main

Closes #1368 (closed) , pytango#660 (closed)

Simple fix. Also add double-set to test.

Edited by Yury Matveev

Merge request reports