The old check_X_source_runs modules did not verify the arguments, so
we cannot start doing it now. Downgrade the hard error introduced in
commit 357e2ef4 (CheckSoureRuns: Add a unified way to check if a
source runs, 2020-09-14) via !5223 (merged) into a noisy warning.
Cc: @robertmaynard
Backport: release