Add shell bash

Author: omus

.github/workflows/ci.yml

@@ -72,6 +72,7 @@ jobs:
       # skipped.
       - name: Test skipping registry cloning of duplicate repos
         if: ${{ matrix.pkg-server == 'pkg.julialang.org' }}
+        shell: bash
         run: |
           if julia -e 'VERSION >= v"1.7-" || exit(1)'; then
               ! test -d $HOME/.julia/registries/General