Update awscli to >= 1.29.4 for pyyaml 6.0 support

[phackstock]

This PR updates the awscli dependency to >=1.29.4. Reason for that is that at this version number pyyaml 6.0 is supported. This is important because after the most recent update of cython, pyyaml < 6.0 no longer works.

• [ ] Tests added
• [ ] Documentation added
• [ ] Example added (in the documentation, to an existing notebook, or in a new notebook)
• [x] Description in CHANGELOG.rst added (single line such as: (`#XX <https://github.com/iiasa/climate-assessment/pull/XX>`_) Added feature which does something)

@jkikstra or @znicholls a quick review would me much appreciated since this is currently blocking me from updating our processing containers.

[phackstock]

God we really made a mess of our pinning the first time around, apologies

Working through it one failing docker build at a time...

Thanks for the quick review @znicholls.