Check that user exists before adding

Author: cunla

.github/workflows/add_member.yml

@@ -36,6 +36,7 @@ jobs:
           python -c "print('USERNAME='+'${{ github.event.issue.title }}'.split(' - ')[1])" >> $GITHUB_ENV
 
       - name: Check whether username exists
+        shell: bash
         env:
           GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}
         run: |