fix(ci): unbound `$PYTHIA8` and deprecate `valgrind` checks #1047

Job	Run time
build_all (release)	1m 29s
delphes_fastsim (1, --version hepmc.pythia6 --no-radcor --limit 5 --num-hepmc-events 150 --minQ2 1)	1m 29s
download_fullsim (epic_latest, --version epic.latest --limit 2 --detector brycecanyon...	1m 15s
build_no_delphes	1m 28s
download_fullsim (epic_previous, --version epic.previous --limit 2 --detector brycecany...	1m 28s
download_fullsim (ecce, --version ecce.22.1 --limit 4)	1m 29s
delphes_fastsim (10, --version hepmc.pythia6 --no-radcor --limit 5 --num-hepmc-events 150 --minQ2...	1m 26s
delphes_fastsim (100, --version hepmc.pythia6 --no-radcor --limit 5 --num-hepmc-events 150 --minQ...	1m 29s
delphes_fastsim (1000, --version hepmc.pythia6 --no-radcor --limit 5 --num-hepmc-events 150 --min...	1m 30s
download_fullsim (athena, --version athena.deathvalley-v1.0 --limit 2)	58s
analysis_fullsim	1s
analysis_fastsim	1s
comparison	1s
postprocess	1s
collect	1s
	14m 6s

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