Update git submodules

Update git submodules

* Update docs/submodules/releng from branch 'master'
  to 9b755e2d6458afec266bd8eb5ebd06083bc11d2c
  - Merge "using global tox verify job"
  - using global tox verify job

    This patch replaces the old rtd verify job, which still defaulted to
    Python 2, with the global tox verify job and a Python 3 environment.

    Signed-off-by: Georg Kunz <georg.kunz@ericsson.com>
    Change-Id: Ic6c1491460a067a930b10e7bdda75701768cdde6