Update git submodules

* Update swift from branch 'master'
  to f77172e2ad6fef4b226637b8ae099a6faf810978
  - CI: pin tox at the project level
    
    No sooner do we fix the gate than tox has a new release that breaks
    it again. Let's give them a bit to settle down; in the mean time, stick
    with 3.x.
    
    See tox-dev/tox#2811
    
    Also simplify our warning suppressions. The message filter is a regex,
    so any prefix of the message will suffice. This allows us to also drop a
    new message seen on CentOS 8:
    
       CryptographyDeprecationWarning: Python 3.6 is no longer
       supported by the Python core team. Therefore, support for
       it is deprecated in cryptography. The next release of
       cryptography (40.0) will be the last to support Python 3.6.
    
    As we've previously seen with cryptography warnings, this can slow down
    our probe tests to the point that they time out.
    
    Change-Id: I316170442c67c1b4a5b87f9a1168cc04ca2417b8