In #11474 we prevented TWZ ranges being iterated over which matched
Ruby's handling of Time ranges and as a consequence `include?` stopped
working with both Time ranges and TWZ ranges. However in
ruby/ruby@b061634 support was added for `include?` to use `cover?` for
'linear' objects. Since we have no way of making Ruby consider TWZ
instances as 'linear' we have to override `Range#include?`.

Fixes #30799.