[ci skip] create a bdt's own env in nightlies

bob/devtools/data/gitlab-ci/nightlies.yaml

@@ -23,7 +23,7 @@ stages:
     # remove ~/.conda if it exists unless it's a mac machine
     - "[ -d ~/.conda ] && [ ! -d /Applications ] && rm -rfv ~/.conda"
     - curl --silent "${BOOTSTRAP}" --output "bootstrap.py"
-    - python3 bootstrap.py -vv channel base
+    - python3 bootstrap.py -vv channel bdt
     - source ${CONDA_ROOT}/etc/profile.d/conda.sh
     - conda activate base
   cache: