.circleci: Add Python 3.9 to CI

Signed-off-by: Eli Uriegas <eliuriegas@fb.com>
(cherry picked from commit b77734d)
Signed-off-by: Eli Uriegas <eliuriegas@fb.com>

.circleci/unittest/linux/scripts/setup_env.sh

@@ -27,6 +27,11 @@ if [ ! -d "${conda_dir}" ]; then
 fi
 eval "$(${conda_dir}/bin/conda shell.bash hook)"
 
+CONDA_CHANNEL_FLAGS=""
+if [[ "${PYTHON_VERSION}" = 3.9 ]]; then
+    CONDA_CHANNEL_FLAGS="-c=conda-forge"
+fi
+
 # 2. Create test environment at ./env
 if [ ! -d "${env_dir}" ]; then
     printf "* Creating a test environment\n"
@@ -36,4 +41,4 @@ conda activate "${env_dir}"
 
 # 3. Install Conda dependencies
 printf "* Installing dependencies (except PyTorch)\n"
-conda env update --file "${this_dir}/environment.yml" --prune
+conda env update ${CONDA_CHANNEL_FLAGS} --file "${this_dir}/environment.yml" --prune