while and until don't restrict variables after them

[asterite]

For example:

a = nil
while a.nil?
  a = 1
end

# This currently is (Int32 | Nil) but should be Int32
p typeof(a) # => (Int32 | Nil)

The workaround is to put a = a.nil! until this is implemented.

The same happens with until:

a = nil
until a
  a = 1
end

p typeof(a) # => (Int32 | Nil)

Extracted from #4239