Exclude testdata from published crate

[weiznich]

This commit removes the test data from the published crate.

Fixes #389

[stanislav-tkach]

Thank you for the pull request! Please ignore the failed MLC job. Personally I would probably use exclude instead of include, but I guess it is OK. Still if you can share you thoughts regarding using include over exclude feel free to share.

[weiznich]

I've gone with include as that also prevents accidentally adding files that exist in the local checkout while publishing.

[stanislav-tkach]

Makes sense, thank you!