Add qualifiers for type variables in generated Erlang typespecs

[dvic]

Starting from OTP 26 erlang/otp#6915, warnings are emitted for unbound type variables, for example:

 -spec try_call_timeout_test() -> {ok, GGA}

We need to replace this unbound type variable with term() so that no warning is emitted.

originally reported in gleam-lang/erlang#46