fix: pin bash shell for setup tool script

Agent-Logs-Url: https://github.com/IntelliTect/EssentialCSharp.Web/sessions/d6590875-922c-45ea-9f77-48dbe7ac66c5

Co-authored-by: BenjaminMichaelis <22186029+BenjaminMichaelis@users.noreply.github.com>

Author: Copilot

.github/workflows/copilot-setup-steps.yml

@@ -49,6 +49,7 @@ jobs:
         uses: docker/setup-buildx-action@v4
 
       - name: Install additional development tools
+        shell: bash
         run: |
           echo "Installing additional tools for Copilot agent environment..."
           if dotnet tool list --global | grep -q 'dotnet-ef'; then