Pin packages from the ucdev staging PPA

Otherwise we can get build errors due not synved yet grub-pc-bin and
grub-efi-amd64-signed, and similarly for shim.

snapcraft.yaml

@@ -18,7 +18,21 @@ assumes:
   - snapd2.59.3
 
 parts:
+  # Temporary workaround until pinning is supported by snapcraft
+  pin-ucdev:
+    plugin: nil
+    override-pull: |
+      # This is run before the pull step of grub part, so we make sure
+      # we get the packages from the PPA.
+      set -x
+      cat <<'EOF' > /etc/apt/preferences.d/ucdev
+      Package: *
+      Pin: release LP-PPA-ucdev-uc-staging-ppa,a=jammy,n=jammy
+      Pin: origin ppa.launchpad.net
+      Pin-Priority: 1000
+      EOF
   grub:
+    after: [ pin-ucdev ]
     plugin: nil
     source: .
     build-packages: