change MM scale factor from x10 to x7

In the final high stats performance validation of the retuned MM digitization, we found eta/phi dependent regions of lower efficiency likely caused by a combination of high thresholds and the magnetic fields impact on the cluster shape (see ATLASRECTS-7835). To mitigate the problem, this MR lowers the threshold so that the less efficient regions are recovered. This update will change the output of the run 3 digi/reco and overlay tests.

cc @iodice @rosati @lucam @kluit @stavrop @mvozak cc @jdandoy @jcatmore @nstyles @christos @jchapman