Fix devcontainer failing because of pyyaml version

[kumaranvpl]

Why are these changes needed?

If we don't explicitly specify pyyaml version, it resolves to an older version which has some issues with installing- yaml/pyyaml#724. The fix is to simply pin the version of pyyaml like pyyaml==6.0.2.

To prevent similar issues from happening in the future, we should use pinned versions for dev dependencies - #453

Related issue number

Closes #460

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