Bump PyYAML to resolve build errors

[bnbry]

Currently some internal services depending on this project can not be built because of an issue with the PyYAML version.

More info here: yaml/pyyaml#601

Various community solutions for other projects have been to move forward guits/ceph@fcf76f6

Before this fix

Collecting PyYAML==5.* (from cassandra-migrate->-r requirements.txt (line 1))
  Using cached PyYAML-5.4.1.tar.gz (175 kB)
  Installing build dependencies ... done
  Getting requirements to build wheel ... error
  error: subprocess-exited-with-error

After the fix the build moves forward here

Collecting PyYAML==6.* (from cassandra-migrate==0.3.5->-r requirements.txt (line 1))
  Obtaining dependency information for PyYAML==6.* from https://files.pythonhosted.org/packages/29/61/bf33c6c85c55bc45a29eee3195848ff2d518d84735eb0e2d8cb42e0d285e/PyYAML-6.0.1-cp310-cp310-manylinux_2_17_x86_64.manylinux2014_x86_64.whl.metadata
  Using cached PyYAML-6.0.1-cp310-cp310-manylinux_2_17_x86_64.manylinux2014_x86_64.whl.metadata (2.1 kB)