overlay profiles: make systemd 261.2 stable

Signed-off-by: Mathieu Tortuyaux <mtortuyaux@microsoft.com>

Author: tormath1

sdk_container/src/third_party/coreos-overlay/profiles/coreos/base/package.accept_keywords

@@ -183,3 +183,5 @@ sys-apps/azure-vm-utils
 
 # Keep versions on both arches in sync.
 =sys-libs/libunwind-1.8.3
+
+=sys-apps/systemd-261.2