use safe load since 3.1 requires it

[idletea]

Ruby 3.0 or 3.1 uses Psych 4.0+, Psych 4.0+ uses safe_load as the default for YAML.load, so now YAML.load will refuse to deserialize, among other things, regexes, which are used in places like this.

Older versions of ruby won't recognize the permitted_classes keyword in load, so we have to use safe_load directly to make things worth across ruby versions.