Also use conda-forge channel for requirements

Author: mdpiper

noxfile.py

@@ -46,7 +46,7 @@ def test_notebooks(session: nox.Session) -> None:
     ] + session.posargs
 
     session.conda_install("nbmake", "pytest", "pytest-xdist", channel=["nodefaults", "conda-forge"])
-    session.conda_install("--file", "lessons/requirements.in")
+    session.conda_install("--file", "lessons/requirements.in", channel=["nodefaults", "conda-forge"])
     session.install("git+https://github.com/csdms/bmi-example-python.git")
 
     session.run(*args)