Update git submodules

* Update requirements from branch 'master'
  to 8b7a53cac1cc1fdcd4ab94aad9a7b7d24362fdc3
  - Blacklist sphinx 3.4.2 because of Flask regressions
    
    Using sphinx version 3.4.2 with Flask and documentation builds results
    in an error:
    
      Exception occurred:
        File "/opt/stack/keystone/.tox/docs/lib/python3.8/site-packages/flask/globals.py", line 38, in _lookup_req_object
          raise RuntimeError(_request_ctx_err_msg)
      RuntimeError: Working outside of request context.
    
    This issue has occured a few times with sphinx in the past and has been
    reported upstream [0][1].
    
    This commit blacklists sphinx 3.4.2 until we get a newer release with a fix.
    
    [0] sphinx-doc/sphinx#8655
    [1] sphinx-doc/sphinx#2796
    
    Partial-Bug: 1910419
    
    Change-Id: Ie80e45571efafe73a553ddd89c5be90fe97bea4d