Documentation: cgroup-v2: eliminate markup warnings

Fix markup warnings in cgroup-v2.rst:

Documentation/admin-guide/cgroup-v2.rst:1509: WARNING: Block quote ends without a blank line; unexpected unindent.
Documentation/admin-guide/cgroup-v2.rst:1511: WARNING: Block quote ends without a blank line; unexpected unindent.
Documentation/admin-guide/cgroup-v2.rst:1512: WARNING: Block quote ends without a blank line; unexpected unindent.

Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Cc: Tejun Heo <tj@kernel.org>
Cc: Li Zefan <lizefan@huawei.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: cgroups@vger.kernel.org
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: linux-doc@vger.kernel.org
Signed-off-by: Tejun Heo <tj@kernel.org>

Documentation/admin-guide/cgroup-v2.rst

@@ -1503,7 +1503,7 @@ protected workload.
 
 The limits are only applied at the peer level in the hierarchy.  This means that
 in the diagram below, only groups A, B, and C will influence each other, and
-groups D and F will influence each other.  Group G will influence nobody.
+groups D and F will influence each other.  Group G will influence nobody::
 
 			[root]
 		/	   |		\