apt: shorten cache validity while upgrading

Force an update when switching distributions

roles/base/tasks/apt.yml

@@ -46,7 +46,7 @@
 - name: Run apt-get update
   apt:
     update_cache: yes
-    cache_valid_time: 1800
+    cache_valid_time: '{{ 1800 if ansible_distribution_release == float_debian_dist else 1 }}'
 
 # When testing, try to make dpkg faster by disabling fsync.
 - name: Speed up dpkg