remove defaults channel

Author: HGWright

.github/workflows/ci-tests.yml

@@ -61,7 +61,7 @@ jobs:
       with:
         miniforge-variant: Mambaforge
         miniforge-version: latest
-        channels: conda-forge,defaults
+        channels: conda-forge
         channel-priority: true
         auto-update-conda: true
         environment-file: "requirements/locks/py${{ matrix.python-version }}-linux-64.lock"