Revert "removed superfluous shell setting"

This reverts commit a15a2eb.

Author: orbeckst

.github/workflows/gh-ci.yaml

@@ -73,6 +73,7 @@ jobs:
         version: ${{ matrix.mdanalysis-version }}
         install-tests: true
         installer:  mamba 
+        shell: bash  -l {0} 
 
     - name: Install package
       run: |