MSVertexTracketTool: Fix incorrect sign in tracklet chi squared calculation

The MSVertex Tracklet fitting had an incorrect sign in the chi squared calculation, causing all tracklet segments to fail reconstruction and no MS Vertices to be produced. This patch changes the sign to the correct value, returning the MSVertex performance to its run 2 behavior.

Fixes ATLASRECTS-7166

(cherry picked from commit 6e0b81d2)

Creating a draft MR as a place to discuss whether this can be added to 24.0. From the MSVx analysis perspective, we'd really like this change to be included in the planned 2024 data re-processing early this year, as without it no MS vertices are produced and we'd like to use the 2024 data to begin Run 3 analysis development. We don't really need any MC re-processing with this change in place, as data-driven methods are used for all backgrounds in the analysis.

Co-authored-by: Michael Revering mireveri@lxplus909.cern.ch