Update git submodules

* Update pbr from branch 'master'
  to 491ce1ab095b122b442de1ce662ebc2e29d27de3
  - Update tox.ini to work with tox 4
    
    Resolve the following warnings:
    
      tox.tox_env.errors.Fail: pass_env values cannot contain whitespace,
      use comma to have multiple values in a single line, invalid values
      found 'PBR_INTEGRATION PIPFLAGS PIPVERSION PBRVERSION REPODIR
      WHEELHOUSE PROJECTS'
    
    Also, reduce down the envlist as tox 4 when run in OpenStack CI is
    also attempting to validate interpreters utilizing the
    --skip-missing-interpreters=false setting [1].
    
    Finally, fix up the integration job so that it passes on Ubuntu 22.04.
    This necessitates removing any Python 2-based dependencies used in the
    these jobs (since these are no longer available on Ubuntu 22.04) and
    removing tests for pip versions that are not compatible with Python 3.10
    (the Python version found on Ubuntu 22.04).
    
    [1] tox-dev/tox#2811
    
    Change-Id: Ib4dbe4e09e269219c08a87f6fb64ad9628b5864a
    Signed-off-by: Stephen Finucane <sfinucan@redhat.com>