Parse error with required kwargs and omitted parens

[pvande]

Given a method definition like this:

def foo arg:
  123
end

mruby 3.3.0 parses the definition as:

def foo(arg: 123)
end

… while C Ruby parses it as:

def foo(arg:)
  123
end

I could find no documentation that suggests this is a deliberate change in behavior.