fix Sheet.add_data_validations typespec

[rodrigues]

Hi 👋

This PR fixes Sheet.add_data_validations typespec, including currently supported use case when instead of a values list the user passes one string with a reference within excel (e.g. "RefSheet!$A$2:$A$32").

The function call will not succeed.

Elixlsx.Sheet.add_data_validations(_sheet :: any(), <<_::8, _::size(1)>>, <<_::8, _::size(1)>>, <<_::8, _::size(1)>>)

breaks the contract
(t(), String.t(), String.t(), [String.t()]) :: t()

Thanks!

[xou]

thank you!