Strip optional metadata from empty default collections

[liamcervante]

Previously, in the example test cases the empty default collection would be returned with the optional metadata embedded even though the default value should be a concrete value. This was fixed in the latest release of go-cty, and so was fixed here by pulling the latest go-cty.

Proposed Changelog Update

Bugs Fixed

• ext/typeexpr: Ensure default values do not have optional metadata attached. This prevents crashes when default values are inserted into concrete go-cty values that have also been stripped of their optional metadata.