Fix env.

Author: tobiasraabe

tox.ini

@@ -5,16 +5,16 @@ envlist = pytest
 usedevelop = true
 
 [testenv:pytest]
+conda_channels =
+    conda-forge
+    nodefaults
 conda_deps =
     cloudpickle
     loky
-    pytask >=0.3.0
+    conda-forge/label/pytask_rc::pytask =0.4.0rc2
     pytest
     pytest-cov
     pytest-xdist
-conda_channels =
-    conda-forge
-    nodefaults
 commands =
     pip install --no-deps -e .
     pytest {posargs}