[POSTPONED] GitLab sender email address for notifications won't be changing effective Monday, March 4th at 17:30h. (ffi: OTG0148869)
Migrate all projects to HepMC3. Probably I updated too many, but let's be consistent.
Note that for Athena I avoided editing
build.sh as I personally don't use it
Related to ATLINFR-4781.