Revert test requirements specification

pyproject.toml

@@ -72,7 +72,6 @@ test = [
     "chex",
     "networkx>=2.5",
     "scikit-learn>=1.0",
-    "scikit-sparse>=0.4.6; python_version < '3.11'",
     "tslearn>=0.5; python_version < '3.11'",
 ]
 docs = [
@@ -177,6 +176,7 @@ legacy_tox_ini = """
     [testenv]
     extras = test
     pass_env = CUDA_*,PYTEST_*,CI
+    deps = py{3.8,3.9,3.10}: scikit-sparse>=0.4.6
     commands_pre =
         gpu: python -I -m pip install "jax[cuda]" -f https://storage.googleapis.com/jax-releases/jax_cuda_releases.html
         jax-latest: python -I -m pip install 'git+https://github.com/google/jax@main'