Fix generating incrementals between 12.5.x and 13.0

After name changes in mar filenames from #40829 (closed), generating incrementals from 12.5.x to 13.0 won't work (except for macos where filenames didn't change).

To make this work, we can update the *-incrementals-release makefile targets to add a script that will go to the signed/12.5.x directory, and add symlinks to add the new filenames. And remove it in 13.0.1.

As discussed in: !788 (comment 2935178)