Update docs.yml (#6493)

Bump python version, pin nr-utils

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Fix docs build CI bug.
- pydocmkardown depends on pydocspec 
-[ pydocspec was updated May
6](https://pypi.org/project/docspec-python/#history) (two days ago), and
includes a problematic dependency (`nr.utils` which is specified as
[nr-utils](https://github.com/NiklasRosenstein/python-docspec/blob/61d3e38c55d290da6197236357e1cdfe818d35b5/docspec-python/pyproject.toml#L14C5-L14C23).
This caused imports to fail.
- current fix is fixing the pydocspec version.
- Also using the opportunity to update the python version 3.8 -> 3.9 for
the docs build 0.2

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## Why are these changes needed?

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## Related issue number

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