pint.error --no-color lint --fail-on=xxx rules
! stdout .
cmp stderr stderr.txt

-- rules/0001.yml --
# empty

-- stderr.txt --
level=INFO msg="Finding all rules to check" paths=["rules"]
level=INFO msg="No rules found, skipping Prometheus discovery"
level=ERROR msg="Fatal error" err="invalid --fail-on value: unknown severity: xxx"
