Use :linenos: for examples in defaults/main.yml to mark them as examples

Related to: debops/docs#159

defaults/main.yml

@@ -108,7 +108,10 @@ apt_cacher_ng__port: 3142
 # IPv6, ...). Using a protocol specific format will create binding(s) only on
 # protocol specific socket(s), e. g.  ``0.0.0.0`` will listen only to IPv4.
 #
-# Example::
+# Examples:
+#
+# .. code-block:: yaml
+#    :linenos:
 #
 #    apt_cacher_ng__bind_address:
 #      - 'localhost'
@@ -131,7 +134,10 @@ apt_cacher_ng__fqdn: 'software-cache.{{ ansible_domain }}'
 # The specification of another HTTP proxy which shall be used for downloads.
 # It can include user name and password but see the manual for limitations.
 #
-# Example::
+# Examples:
+#
+# .. code-block:: yaml
+#    :linenos:
 #
 #    apt_cacher_ng__proxy: 'https://username:[email protected]:3129'
 #
@@ -144,7 +150,10 @@ apt_cacher_ng__proxy: ''
 # Specifies the IP protocol families to use for remote connections. Order does
 # matter, first specified are considered first.
 #
-# Example::
+# Examples:
+#
+# .. code-block:: yaml
+#    :linenos:
 #
 #    apt_cacher_ng__connect_protocol:
 #      - 'v4'