Update git submodules

* Update docs/submodules/releng from branch 'master'
  to a250568fc5c4dd1bcb09ef789802e670d6102bfe
  - Remove bionic which is end of life

    https://ubuntu.com/about/release-cycle

    Change-Id: I21ecab94d4ec2ff60120d5b3e271002401002db7
    Signed-off-by: Cédric Ollivier <cedric.ollivier@orange.com>

diff --git a/docs/submodules/releng b/docs/submodules/releng
index 333fd2f..a250568 160000 (submodule)
--- a/docs/submodules/releng
+++ b/docs/submodules/releng
@@ -1 +1 @@
-Subproject commit 333fd2fd83e30492c562ed163c192a4c9111f18b
+Subproject commit a250568fc5c4dd1bcb09ef789802e670d6102bfe