install snapd and update

.github/workflows/armhf_lxd.yaml

@@ -35,6 +35,7 @@ jobs:
           # publicly in your project's package repository, so it is vital that
           # no secrets are present in the container state or logs.
           install: |
+            apt-get update
             apt-get install -y -qq snapd
             snap install lxd snapcraft
             lxd init --auto