Release GIL in Python bindings.
Release GIL in Python bindings.

We apply the same changes as:
https://github.com/google/jsonnet/pull/814

sbarzowski/go-jsonnet,sbarzowski/go-jsonnet,google/go-jsonnet,google/go-jsonnet,sbarzowski/go-jsonnet,google/go-jsonnet,sbarzowski/go-jsonnet,google/go-jsonnet,google/go-jsonnet,sbarzowski/go-jsonnet