fix(deps): update dependency pydata-sphinx-theme to ~0.20.0

[ibm-mend-app]

This PR contains the following updates:

Package	Change	Age	Confidence
pydata-sphinx-theme	~0.9 → ~0.20.0

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[ibm-mend-app]

⚠ Artifact update problem

Renovate failed to update an artifact related to this branch. You probably do not want to merge this PR as-is.

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The artifact failure details are included below:

File name: poetry.lock

Updating dependencies
Resolving dependencies...


The current project's supported Python range (>=3.8,<4.0) is not compatible with some of the required packages Python requirement:
  - pydata-sphinx-theme requires Python >=3.9, so it will not be satisfied for Python >=3.8,<3.9
  - pydata-sphinx-theme requires Python >=3.9, so it will not be satisfied for Python >=3.8,<3.9
  - pydata-sphinx-theme requires Python >=3.9, so it will not be satisfied for Python >=3.8,<3.9

Because no versions of pydata-sphinx-theme match >=0.15.0,<0.15.1 || >0.15.1,<0.15.2 || >0.15.2,<0.15.3 || >0.15.3,<0.16.0
 and pydata-sphinx-theme (0.15.1) requires Python >=3.9, pydata-sphinx-theme is forbidden.
And because pydata-sphinx-theme (0.15.2) requires Python >=3.9, pydata-sphinx-theme is forbidden.
So, because pydata-sphinx-theme (0.15.3) requires Python >=3.9
 and skillsnetwork depends on pydata-sphinx-theme (~0.15.0), version solving failed.

  • Check your dependencies Python requirement: The Python requirement can be specified via the `python` or `markers` properties
    
    For pydata-sphinx-theme, a possible solution would be to set the `python` property to ">=3.9,<4.0"
    For pydata-sphinx-theme, a possible solution would be to set the `python` property to ">=3.9,<4.0"
    For pydata-sphinx-theme, a possible solution would be to set the `python` property to ">=3.9,<4.0"

    https://python-poetry.org/docs/dependency-specification/#python-restricted-dependencies,
    https://python-poetry.org/docs/dependency-specification/#using-environment-markers