pacman: don't always return changed w/ update_cache (#4318) (#4322)

* pacman: don't always return changed w/ update_cache

This used to be the behavior before the recent refactoring. [1]

Allows the following to return changed only when packages were upgraded:

  - pacman:
    update_cache: yes
    upgrade: yes

And the following to return changed only when the foo package wasn't at
the latest version:

  - pacman:
    name: foo
    state: latest
    update_cache: yes

[1] https://github.com/ansible-collections/community.general/pull/3907

* Update changelogs/fragments/4318-pacman-restore-old-changed-behavior.yml

Co-authored-by: Felix Fontein <felix@fontein.de>

Co-authored-by: Felix Fontein <felix@fontein.de>
(cherry picked from commit cc8151f209)

Co-authored-by: Evangelos Foutras <evangelos@foutrelis.com>

changelogs/fragments/4318-pacman-restore-old-changed-behavior.yml

@@ -0,0 +1,12 @@
+bugfixes:
+  - pacman - when the ``update_cache`` option is combined with another option
+    such as ``upgrade``, report ``changed`` based on the actions performed by
+    the latter option. This was the behavior in community.general 4.4.0 and before.
+    In community.general 4.5.0, a task combining these options would always
+    report ``changed``
+    (https://github.com/ansible-collections/community.general/pull/4318).
+
+known_issues:
+   - pacman - ``update_cache`` cannot differentiate between up to date and
+     outdated package lists and will report ``changed`` in both situations
+     (https://github.com/ansible-collections/community.general/pull/4318).