remove mamba from ci_test workflow

Author: Mark Wieczorek

.github/workflows/ci_test.yml

@@ -29,7 +29,6 @@ jobs:
       uses: conda-incubator/setup-miniconda@v3
       with:
         python-version: ${{ matrix.python-version }}
-        mamba-version: "*"
         channels: conda-forge
         channel-priority: strict
         auto-update-conda: true