updated GWSkyNet to use ligo.skymap-v2.1.1

This merge request does the following:

Update GWSkyNet from version 2.4.1 to 2.5.1 to be compatible with ligo.skymap 2.1.1 (see !1528 (closed)). Given GWSkyNet v2.4.1 is flagged as an issue that blocks unit tests for python 3.12, I have also taken the liberty of updating GWSkyNet and to remove the upper limit on tensorflow-cpu (see !1532 (merged)). This will also solve #774 and !1528 (closed).

I am making this as a draft at the moment as I just asked the GWSkyNet review team to review the changes. An SCCB ticket will be created once the review is completed.