Fix baremetal jobs on Ubuntu 20.04

Add workaround to grub-efi-amd64-signed package
See [1][2]

[1] https://askubuntu.com/questions/1276111/error-upgrading-grub-efi-amd64-signed-special-device-old-ssd-does-not-exist
[2] https://forum.hestiacp.com/t/ubuntu-20-04-installation-error/4323

.github/workflows/functional-baremetal.yaml

@@ -40,6 +40,10 @@ jobs:
     steps:
       - name: Checkout Gophercloud
         uses: actions/checkout@v4
+      - name: Workaround for grub-efi-amd64-signed
+        run: sudo apt update && sudo apt -y upgrade
+        shell: bash
+        if: ${{ matrix.ubuntu_version == "20.04" }}
       - name: Deploy devstack
         uses: EmilienM/[email protected]
         with: