856 Add fix to be able to create current environment on MacOS 13.3.1

#856

[author: paolafer]

There were problems creating the 3.8-2022-4-13 environment and this
fix by Corey Adams solves it.

[reviewer: gonzaponte]

I beleive this is ok and does not disrupt the installation process in
other machines.

NOTE: Title shortened to match formatting.

manage.sh

@@ -83,6 +83,9 @@ function make_environment {
 
     cat <<EOF > ${YML_FILENAME}
 name: ${CONDA_ENV_NAME}
+channels:
+- conda-forge
+- defaults
 dependencies:
 - python       = ${PYTHON_VERSION}
 # *REMEMBER TO CHANGE CONDA_ENV_TAG WHEN CHANGING VERSION NUMBERS*