ansible: Ensure sources.list is properly set

ansible/roles/pds_deb/tasks/main.yml

+- name: "Apt sources list"
+  copy:
+    dest: /etc/apt/sources.list
+    content:
+      deb http://ftp.fi.muni.cz/pub/linux/debian/ bullseye main contrib non-free
+      deb-src http://ftp.fi.muni.cz/pub/linux/debian/ bullseye main contrib non-free
+
+      deb http://security.debian.org/ bullseye-security main contrib non-free
+      deb-src http://security.debian.org/ bullseye-security main contrib non-free
+  register: apt_sources
+
+- name: "Update apt cache after source update"
+  apt:
+    update_cache: true
+  when: apt_sources.changed
+
 - name: Create /var/obj
   file:
     state: directory