tests: skip data structures fuzzing tests unless environment variable set
tests: skip data structures fuzzing tests unless environment variable set

We do this for all other fuzz tests.
terrelln/python-zstandard,terrelln/python-zstandard,indygreg/python-zstandard,terrelln/python-zstandard,terrelln/python-zstandard,indygreg/python-zstandard,indygreg/python-zstandard,indygreg/python-zstandard